Magnetic tape, magnetic tape cartridge, and magnetic tape device

ABSTRACT

The magnetic tape includes a non-magnetic support, and a magnetic layer containing a ferromagnetic powder, in which an edge portion Ra which is an arithmetic average roughness Ra measured at an edge portion of a surface of the magnetic layer is 1.50 nm or less, a central portion Ra which is an arithmetic average roughness Ra measured at a central portion of the surface of the magnetic layer is 0.30 nm to 1.30 nm, and a Ra ratio (central portion Ra/edge portion Ra) is 0.75 to 0.95.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2021-156586 filed on Sep. 27, 2021. The aboveapplication is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape, a magnetic tapecartridge, and a magnetic tape device.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recordingmedia and disk-shaped magnetic recording media, and tape-shaped magneticrecording media, that is, magnetic tapes are mainly used for datastorage such as data back-up or archives (for example, seeJP2016-524774A and US2019/0164573A1).

SUMMARY OF THE INVENTION

The recording of data on a magnetic tape is normally performed bycausing the magnetic tape to run in a magnetic tape device and causing amagnetic head to follow a data band of the magnetic tape to record dataon the data band. Accordingly, a data track is formed on the data band.In addition, in a case of reproducing the recorded data, normally, themagnetic tape is caused to run in the magnetic tape device and themagnetic head is caused to follow the data band of the magnetic tape,thereby reading data recorded on the data band.

In order to increase an accuracy with which the magnetic head followsthe data band of the magnetic tape in the recording and/or thereproducing, a system that performs head tracking using a servo signal(hereinafter, referred to as a “servo system”) is practiced.

In addition, it is proposed that dimensional information of a magnetictape during running in a width direction (contraction, expansion, or thelike) is obtained using the servo signal and an angle for tilting anaxial direction of a module of a magnetic head with respect to the widthdirection of the magnetic tape (hereinafter, also referred to as a “headtilt angle”) is changed according to the obtained dimensionalinformation (see JP6590102B and US2019/0164573A1, for example,paragraphs 0059 to 0067 and paragraph 0084 of JP6590102B). During therecording or the reproducing, in a case where the magnetic head forrecording or reproducing data records or reproduces data while beingdeviated from a target track position due to width deformation of themagnetic tape, phenomenons such as overwriting on recorded data,reproducing failure, and the like may occur. The present inventorsconsider that changing the head tilt angle as described above is one ofa unit for suppressing the occurrence of such a phenomenon.

For example, assuming that the head tilt angle is changed as describedabove, it is desirable that running stability of the magnetic tape ishigh, in a case of recording and/or reproducing data at different headtilt angles. It is considered that the high running stability of themagnetic tape can lead to, for example, the further suppressing of theoccurrence of the phenomenon described above.

Meanwhile, in recent years, magnetic tapes may be used in temperatureand humidity managed data centers.

Meanwhile, in the data center, power saving is necessary for reducingthe cost. For realizing the power saving, it is desired that themanagement conditions of an use environment of the magnetic tape in thedata center can be relaxed compared to the current state, or themanaging may not be necessary.

However, it is also assumed that, in a case where the managementconditions of the use environment are relaxed or not managed, themagnetic tape is used, for example, in a high temperature and lowhumidity environment. Accordingly, a magnetic tape having excellentrunning stability in a case of recording and/or reproducing data atdifferent head tilt angles in a high temperature and low humidityenvironment is desirable.

One aspect of the present invention is to provide a magnetic tape havingexcellent running stability in a case of recording and/or reproducingdata at different head tilt angles in a high temperature and lowhumidity environment.

According to an aspect of the invention, there is provided a magnetictape comprising: a non-magnetic support; and a magnetic layer containinga ferromagnetic powder, in which an edge portion Ra which is anarithmetic average roughness Ra measured at an edge portion of a surfaceof the magnetic layer is 1.50 nm or less, a central portion Ra which isan arithmetic average roughness Ra measured at a central portion of thesurface of the magnetic layer is 0.30 nm to 1.30 nm, and a Ra ratio(central portion Ra/edge portion Ra) is 0.75 to 0.95.

In one embodiment, the magnetic tape may further include a non-magneticlayer containing a non-magnetic powder between the non-magnetic supportand the magnetic layer.

In one embodiment, the non-magnetic powder may contain a Fe-basedinorganic oxide powder having an average particle volume of 2.0×10⁻⁶ μm³or less.

In one embodiment, the non-magnetic powder may contain carbon blackhaving a pH of 5.0 or less.

In one embodiment, a standard deviation of curvature of the magnetictape in a longitudinal direction may be 5 mm/m or less.

In one embodiment, the magnetic tape may include a back coating layercontaining a non-magnetic powder on a surface side of the non-magneticsupport opposite to a surface side provided with the magnetic layer.

In one embodiment, the magnetic tape may have a tape thickness of 5.2 μmor less.

In one embodiment, a vertical squareness ratio of the magnetic tape maybe 0.60 or more.

According to another aspect of the invention, there is provided amagnetic tape cartridge comprising the magnetic tape described above.

According to still another aspect of the invention, there is provided amagnetic tape device comprising the magnetic tape.

In one embodiment, the magnetic tape device may further comprise amagnetic head, the magnetic head may include a module including anelement array having a plurality of magnetic head elements between apair of servo signal reading elements, and the magnetic tape device maychange an angle θ formed by an axis of the element array with respect toa width direction of the magnetic tape during running of the magnetictape in the magnetic tape device.

According to one aspect of the present invention, it is possible toprovide a magnetic tape having excellent running stability in a case ofrecording and/or reproducing data at different head tilt angles in ahigh temperature and low humidity environment. In addition, according toone aspect of the invention, it is possible to provide a magnetic tapecartridge and a magnetic tape device including the magnetic tape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an example of a module of a magnetichead.

FIG. 2 is an explanatory diagram of a relative positional relationshipbetween a module and a magnetic tape during running of the magnetic tapein a magnetic tape device.

FIG. 3 is an explanatory diagram of a change in angle θ during therunning of the magnetic tape.

FIG. 4 is an explanatory diagram of a curvature of a magnetic tape in alongitudinal direction.

FIG. 5 shows an example of disposition of data bands and servo bands.

FIG. 6 shows a servo pattern disposition example of a linear tape-open(LTO) Ultrium format tape.

FIG. 7 is an explanatory diagram of a method for measuring the angle θduring the running of the magnetic tape.

FIG. 8 is a schematic view showing an example of the magnetic tapedevice.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Magnetic Tape

An aspect of the invention relates to a magnetic tape including anon-magnetic support, and a magnetic layer containing a ferromagneticpowder. An arithmetic average roughness Ra measured at an edge portionof a surface of the magnetic layer is referred to as an edge portion Ra,and an arithmetic average roughness Ra measured at a central portion ofthe surface of the magnetic layer is referred to as a central portionRa. In the magnetic tape described above, the edge portion Ra is 1.50 nmor less, the central portion Ra is 0.30 to 1.30 nm, and a Ra ratio(central portion Ra/edge portion Ra) is 0.75 to 0.95. In the inventionand the specification, the “surface of the magnetic layer” is identicalto a surface of the magnetic tape on the magnetic layer side.

Description of Head Tilt Angle

Hereinafter, prior to the description of the magnetic tape, aconfiguration of the magnetic head, a head tilt angle, and the like willbe described. In addition, a reason why it is considered that thephenomenon occurring during the recording or during the reproducingdescribed above can be suppressed by tilting an axial direction of themodule of the magnetic head with respect to the width direction of themagnetic tape while the magnetic tape is running will also be describedlater.

The magnetic head may include one or more modules including an elementarray including a plurality of magnetic head elements between a pair ofservo signal reading elements, and can include two or more modules orthree or more modules. The total number of such modules can be, forexample, 5 or less, 4 or less, or 3 or less, or the magnetic head mayinclude the number of modules exceeding the total number exemplifiedhere. Examples of arrangement of the plurality of modules can include“recording module-reproducing module” (total number of modules: 2),“recording module-reproducing module-recording module” (total number ofmodules: 3), and the like. However, the invention is not limited to theexamples shown here.

Each module can include an element array including a plurality ofmagnetic head elements between a pair of servo signal reading elements,that is, arrangement of elements. The module including a recordingelement as the magnetic head element is a recording module for recordingdata on the magnetic tape. The module including a reproducing element asthe magnetic head element is a reproducing module for reproducing datarecorded on the magnetic tape. In the magnetic head, the plurality ofmodules are arranged, for example, in a recording and reproducing headunit so that an axis of the element array of each module is oriented inparallel. The “parallel” does not mean only parallel in the strictsense, but also includes a range of errors normally allowed in thetechnical field of the invention. For example, the range of errors meansa range of less than ±10° from an exact parallel direction.

In each element array, the pair of servo signal reading elements and theplurality of magnetic head elements (that is, recording elements orreproducing elements) are usually arranged to be in a straight linespaced apart from each other. Here, the expression that “arranged in astraight line” means that each magnetic head element is arranged on astraight line connecting a central portion of one servo signal readingelement and a central portion of the other servo signal reading element.The “axis of the element array” in the present invention and the presentspecification means the straight line connecting the central portion ofone servo signal reading element and the central portion of the otherservo signal reading element.

Next, the configuration of the module and the like will be furtherdescribed with reference to the drawings. However, the embodiment shownin the drawings is an example and the invention is not limited thereto.

FIG. 1 is a schematic view showing an example of a module of a magnetichead. The module shown in FIG. 1 includes a plurality of magnetic headelements between a pair of servo signal reading elements (servo signalreading elements 1 and 2). The magnetic head element is also referred toas a “channel”. “Ch” in the drawing is an abbreviation for a channel.The module shown in FIG. 1 includes a total of 32 magnetic head elementsof Ch0 to Ch31.

In FIG. 1 , “L” is a distance between the pair of servo signal readingelements, that is, a distance between one servo signal reading elementand the other servo signal reading element. In the module shown in FIG.1 , the “L” is a distance between the servo signal reading element 1 andthe servo signal reading element 2. Specifically, the “L” is a distancebetween a central portion of the servo signal reading element 1 and acentral portion of the servo signal reading element 2. Such a distancecan be measured by, for example, an optical microscope or the like.

FIG. 2 is an explanatory diagram of a relative positional relationshipbetween the module and the magnetic tape during running of the magnetictape in the magnetic tape device. In FIG. 2 , a dotted line A indicatesa width direction of the magnetic tape. A dotted line B indicates anaxis of the element array. An angle θ can be the head tilt angle duringthe running of the magnetic tape, and is an angle formed by the dottedline A and the dotted line B. During the running of the magnetic tape,in a case where the angle θ is 0°, a distance in a width direction ofthe magnetic tape between one servo signal reading element and the otherservo signal reading element of the element array (hereinafter, alsoreferred to as an “effective distance between servo signal readingelements”) is “L”. On the other hand, in a case where the angle θexceeds 0°, the effective distance between the servo signal readingelements is “L cos θ” and the L cos θ is smaller than the L. That is, “Lcos θ<L”.

As described above, during the recording or the reproducing, in a casewhere the magnetic head for recording or reproducing data records orreproduces data while being deviated from a target track position due towidth deformation of the magnetic tape, phenomenons such as overwritingon recorded data, reproducing failure, and the like may occur. Forexample, in a case where a width of the magnetic tape contracts orextends, a phenomenon may occur in which the magnetic head element thatshould record or reproduce at a target track position records orreproduces at a different track position. In addition, in a case wherethe width of the magnetic tape extends, the effective distance betweenthe servo signal reading elements may be shortened than a spacing of twoadjacent servo bands with a data band interposed therebetween (alsoreferred to as a “servo band spacing” or “spacing of servo bands”,specifically, a distance between the two servo bands in the widthdirection of the magnetic tape), and a phenomenon in that the data isnot recorded or reproduced at a part close to an edge of the magnetictape can occur.

With respect to this, in a case where the element array is tilted at theangle θ exceeding 0°, the effective distance between the servo signalreading elements becomes “L cos θ” as described above. The larger thevalue of 0, the smaller the value of L cos θ, and the smaller the valueof θ, the larger the value of L cos θ. Accordingly, in a case where thevalue of θ is changed according to a degree of dimension change (thatis, contraction or expansion) in the width direction of the magnetictape, the effective distance between the servo signal reading elementscan be brought closer to or matched with the spacing of the servo bands.Therefore, during the recording or the reproducing, it is possible toprevent the occurrence of phenomenons such as overwriting on recordeddata, reproducing failure, and the like caused in a case where themagnetic head for recording or reproducing data records or reproducesdata while being deviated from a target track position due to widthdeformation of the magnetic tape, or it is possible to reduce afrequency of occurrence thereof.

FIG. 3 is an explanatory diagram of a change in angle θ during therunning of the magnetic tape.

The angle θ at the start of running, θ_(initial), can be set to, forexample, 0° or more or more than 0°.

In FIG. 3 , a central diagram shows a state of the module at the startof running.

In FIG. 3 , a right diagram shows a state of the module in a case wherethe angle θ is set to an angle θ_(c) which is a larger angle than theθ_(initial). The effective distance between the servo signal readingelements L cos θ_(c) is a value smaller than L cos θ_(initial) at thestart of running of the magnetic tape. In a case where the width of themagnetic tape is contracted during the running of the magnetic tape, itis preferable to perform such angle adjustment.

On the other hand, in FIG. 3 , a left diagram shows a state of themodule in a case where the angle θ is set to an angle θ_(e) which is asmaller angle than the θ_(initial). The effective distance between theservo signal reading elements L cos θ_(e) is a value larger than L cosθ_(initial) at the start of running of the magnetic tape. In a casewhere the width of the magnetic tape is expanded during the running ofthe magnetic tape, it is preferable to perform such angle adjustment.

As described above, the change of the head tilt angle during the runningof the magnetic tape can contribute to prevention of the occurrence ofphenomenons such as overwriting on recorded data, reproducing failure,and the like caused in a case where the magnetic head for recording orreproducing data records or reproduces data while being deviated from atarget track position due to width deformation of the magnetic tape, orto reduction of a frequency of occurrence thereof.

Meanwhile, the recording of data on the magnetic tape and thereproducing of the recorded data are performed by bringing the surfaceof the magnetic layer of the magnetic tape into contact with themagnetic head and sliding. The inventors considered that, during suchsliding, in a case where the head tilt angle changes, a contact statebetween the magnetic head and the surface of the magnetic layer canchange and this can be a reason of a decrease in running stability.Specifically, the inventors surmised that, in a case where the contactstate between the surface of the magnetic layer of the magnetic tape andthe magnetic head (for example, a contact state between a portion nearan edge of the module of the magnetic head and the edge portion of thesurface of the magnetic layer) changes greatly depending on thedifference in the head tilt angle, the running stability decreases andsuch decrease in running stability can become more remarkable in a hightemperature and low humidity environment. However, the present inventionis not limited to the inference of the inventors described in thepresent specification.

Based on the surmise described above, the present inventors conductedintensive studies. As a result, the inventors newly found that,regarding surface properties of the surface of the magnetic layer of themagnetic tape, by making a surface roughness of the edge portion rougherthan a surface roughness of the central portion, specifically, bysetting each of the edge portion Ra, the central portion Ra, and the Raratio (central portion Ra/edge portion Ra) to be within the rangesdescribed above, it is possible to improve the running stability in acase of performing the recording and/or reproducing of data at differenthead tilt angles in the high temperature and low humidity environment.

In the following, the running stability in a case of performing therecording and/or reproducing of data by changing the head tilt angleduring the running of the magnetic tape in the high temperature and lowhumidity environment is also simply referred to as “running stability”.In addition, the high temperature and low humidity environment can be,for example, an environment having a temperature of approximately 30° C.to 50° C. A humidity of the environment can be, for example,approximately 0% to 30% as a relative humidity. The temperatures and thehumidity described for the environment in the specification are anatmosphere temperature and a relative humidity of such an environment.

Edge Portion Ra, Central Portion Ra, Ra Ratio (Central Portion Ra/EdgePortion Ra)

In the present invention and the present specification, the arithmeticaverage roughness Ra is measured by a noncontact optical surfaceroughness meter. The measurement conditions and data processingconditions are as follows. As the noncontact optical surface roughnessmeter, for example, Bruker's noncontact optical surface roughness meterContour can be used, and in examples which will be described later, thisnoncontact optical surface roughness meter was used.

Measurement Conditions

Measurement environment: Temperature of 23° C. and relative humidity of50%

Measurement mode: Phase Shift Interferometry (PSI)

Objective lens: 10×

Intermediate lens: 1.0×

Visual field for measurement: 355 μm×474 μm

Data Processing Conditions

Distortion/tilt correction: Cylinder and Tilt (Zero Level: Zero Mean)

Filter: Gaussian

-   -   Band Pass: Order=0    -   Type=Regular    -   High Pass Filter=1.11 μm    -   Low Pass Filter=50 μm

In the present invention and the present specification, the edge portionRa which is the arithmetic average roughness Ra measured at the edgeportion of the surface of the magnetic layer is a value obtained by thefollowing method.

Both ends of the magnetic tape in the width direction are called edges.

At an arbitrary position on the surface of the magnetic layer of themagnetic tape to be measured, one edge is included in the visual fieldfor measurement, and measurement is performed with the noncontactoptical surface roughness meter under the measurement conditionsdescribed above.

After data processing is performed on the obtained measurement resultsunder the data processing conditions described above, a range of 200 μmin width×200 μm in length (that is, distance of the magnetic tape in thelongitudinal direction) is designated at an arbitrary position in thevisual field for measurement, in a region having a width of 200 μm froma “position of an inner side of 50 μm from the edge” to a “position ofan inner side of 200 μm further from the position of the inner side of50 μm from the edge”, and the Ra of the designated range is obtained. Ananalysis unit provided in the noncontact optical surface roughness metercan calculate and output the Ra.

Then, the other edge is included in the visual field for measurement andthe Ra is obtained by the method described above.

For each of the one edge side and the other edge side, the measurementis performed three times in total by shifting the measurement positionby 1 mm or more.

By the measurement described above, a total of 6 Ras are obtained. Thearithmetic average of the Ras obtained accordingly is defined as theedge portion Ra.

In the present invention and the present specification, the centralportion Ra which is the arithmetic average roughness Ra measured at thecentral portion of the surface of the magnetic layer is a value obtainedby the following method.

On the surface of the magnetic layer, for one edge randomly selectedfrom both edges of the magnetic tape, a range of 200 μm in width×200 μmin length is designated at an arbitrary position in the visual field formeasurement, in a region having a width of 6 mm from a “position of aninner side of 3 mm from the edge” to a “position of an inner side of 6mm further from the position of the inner side of 3 mm from the edge”,and the Ra of the designated range is obtained. For the edge sideselected above, the measurement is performed six times in total byshifting the measurement position by 1 mm or more.

By the measurement described above, a total of 6 Ras are obtained. Thearithmetic average of the Ras obtained accordingly is defined as thecentral portion Ra.

The Ra ratio (central portion Ra/edge portion Ra) is calculated from theedge portion Ra and the central portion Ra obtained by the methoddescribed above. In the magnetic tape described above, the Ra ratio(central portion Ra/edge portion Ra) is 0.75 or more, preferably 0.77 ormore, and more preferably 0.80 or more, from a viewpoint of improvingthe running stability in a case of performing the recording and/orreproducing of data at different head tilt angles in the hightemperature and low humidity environment. In addition, from theviewpoint described above, the Ra ratio (central portion Ra/edge portionRa) is 0.95 or less, preferably 0.93 or less, and more preferably 0.90or less.

In the magnetic tape described above, the edge portion Ra is 1.50 nm orless, preferably 1.30 nm or less, more preferably 1.00 nm or less, evenmore preferably 0.95 nm or less, and still preferably 0.90 nm or less,from a viewpoint of improving the running stability. The edge portion Racan be, for example, 0.10 nm or more, 0.20 nm or more, or 0.30 nm ormore, or can be less than the value exemplified here.

In the magnetic tape, the central portion Ra is 1.30 nm or less,preferably 1.20 nm or less, more preferably 1.10 nm or less, even morepreferably 1.00 nm or less, still preferably 0.90 nm or less, and stillmore preferably 0.80 nm or less, from a viewpoint of improving therunning stability. In addition, from the viewpoint described above, thecentral portion Ra is 0.30 nm or more, preferably 0.40 nm or more, andmore preferably 0.50 nm or more.

A control method of the Ra ratio, the edge portion Ra, and the centralportion Ra will be described later.

Standard Deviation of Curvature

Next, a standard deviation of a curvature will be described.

The curvature of the magnetic tape in the longitudinal direction of thepresent invention and the present specification is a value obtained bythe following method in an environment of an atmosphere temperature of23° C. and a relative humidity of 50%. The magnetic tape is normallyaccommodated and circulated in a magnetic tape cartridge. As themagnetic tape to be measured, a magnetic tape taken out from an unusedmagnetic tape cartridge that is not attached to the magnetic tape deviceis used.

FIG. 4 is an explanatory diagram of the curvature of the magnetic tapein the longitudinal direction.

A tape sample having a length of 100 m in the longitudinal direction iscut out from a randomly selected portion of the magnetic tape to bemeasured. One end of this tape sample is defined as a position of 0 m,and a position spaced apart from this one end toward the other end by Dm (D meters) in the longitudinal direction is defined as a position of Dm. Accordingly, a position spaced apart by 10 m in the longitudinaldirection is defined as a position of 10 m, a position spaced apart by20 m is defined as a position of 20 m, and in this manner, a position of30 m, a position of 40 m, a position of 50 m, a position of 60 m, aposition of 70 m, a position of 80 m, a position of 90 m, and a positionof 100 m are defined at intervals of 10 m sequentially.

A tape sample having a length of 1 m from the 0 m position to theposition of 1 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 0 m.

A tape sample having a length of 1 m from the 10 m position to theposition of 11 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 10 m.

A tape sample having a length of 1 m from the 20 m position to theposition of 21 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 20 m.

A tape sample having a length of 1 m from the 30 m position to theposition of 31 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 30 m.

A tape sample having a length of 1 m from the 40 m position to theposition of 41 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 40 m.

A tape sample having a length of 1 m from the 50 m position to theposition of 51 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 50 m.

A tape sample having a length of 1 m from the 60 m position to theposition of 61 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 60 m.

A tape sample having a length of 1 m from the 70 m position to theposition of 71 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 70 m.

A tape sample having a length of 1 m from the 80 m position to theposition of 81 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 80 m.

A tape sample having a length of 1 m from the 90 m position to theposition of 91 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 90 m.

A tape sample having a length of 1 m from the 99 m position to theposition of 100 m is cut out. This tape sample is used as a tape samplefor measuring the curvature at the position of 100 m.

The tape sample of each position is hung for 24 hours±4 hours in atension-free state by gripping an upper end portion with a grippingmember (clip or the like) by setting the longitudinal direction as thevertical direction. Then, within 1 hour, the following measurement isperformed.

As shown in FIG. 4 , the tape piece is placed on a flat surface in atension-free state. The tape piece may be placed on a flat surface withthe surface on the magnetic layer side facing upward, or may be placedon a flat surface with the other surface facing upward. In FIG. 4 , Sindicates a tape sample and W indicates the width direction of the tapesample. Using an optical microscope, a distance L1 (unit: mm) that is ashortest distance between a virtual line 54 connecting both terminalportions 52 and 53 of the tape sample S and a maximum curved portion 55in the longitudinal direction of the tape sample S is measured. FIG. 4shows an example in which the tape sample is curved upward on a papersurface. Even in a case where the tape sample is curved downward, thedistance L1 (mm) is measured in the same manner. The distance L1 isdisplayed as a positive value regardless of which side is curved. In acase where no curve in the longitudinal direction is confirmed, the L1is set to 0 (zero) mm.

By doing so, a standard deviation of the curvature L1 measured for atotal of 11 positions from the position of 0 m to the position of 100 m(that is, a positive square root of the dispersion) is the standarddeviation of the curvature of the magnetic tape to be measured in thelongitudinal direction (unit: mm/m).

In the magnetic tape, the standard deviation of the curvature obtainedby the method described above can be, for example, 7 mm/m or less and 6mm/m or less, and from a viewpoint of further improving the runningstability, it is preferably 5 mm/m or less, more preferably 4 mm/m orless, and even more preferably 3 mm/m or less. The standard deviation ofthe curvature of the magnetic tape can be, for example, 0 mm/m or more,more than 0 mm/m, 1 mm/m or more, or 2 mm/m or more. It is preferablethat the value of the standard deviation of the curvature is small, froma viewpoint of further improving the running stability.

The standard deviation of the curvature can be controlled by adjustingthe manufacturing conditions of the manufacturing step of the magnetictape. This point will be described later in detail.

Hereinafter, the magnetic tape will be described more specifically.

Magnetic Layer

Ferromagnetic Powder

As the ferromagnetic powder contained in the magnetic layer, awell-known ferromagnetic powder can be used as one kind or incombination of two or more kinds as the ferromagnetic powder used in themagnetic layer of various magnetic recording media. It is preferable touse a ferromagnetic powder having an average particle size as theferromagnetic powder, from a viewpoint of improvement of a recordingdensity. From this viewpoint, an average particle size of theferromagnetic powder is preferably equal to or smaller than 50 nm, morepreferably equal to or smaller than 45 nm, even more preferably equal toor smaller than 40 nm, further preferably equal to or smaller than 35nm, further more preferably equal to or smaller than 30 nm, further evenmore preferably equal to or smaller than 25 nm, and still preferablyequal to or smaller than 20 nm. Meanwhile, from a viewpoint of stabilityof magnetization, the average particle size of the ferromagnetic powderis preferably equal to or greater than 5 nm, more preferably equal to orgreater than 8 nm, even more preferably equal to or greater than 10 nm,still preferably equal to or greater than 15 nm, and still morepreferably equal to or greater than 20 nm.

Hexagonal Ferrite Powder

As a preferred specific example of the ferromagnetic powder, a hexagonalferrite powder can be used. For details of the hexagonal ferrite powder,descriptions disclosed in paragraphs 0012 to 0030 of JP2011-225417A,paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 ofJP2012-204726A, and paragraphs 0029 to 0084 of JP2015-127985A can bereferred to, for example.

In the invention and the specification, the “hexagonal ferrite powder”is a ferromagnetic powder in which a hexagonal ferrite type crystalstructure is detected as a main phase by X-ray diffraction analysis. Themain phase is a structure to which a diffraction peak at the highestintensity in an X-ray diffraction spectrum obtained by the X-raydiffraction analysis belongs. For example, in a case where thediffraction peak at the highest intensity in the X-ray diffractionspectrum obtained by the X-ray diffraction analysis belongs to ahexagonal ferrite type crystal structure, it is determined that thehexagonal ferrite type crystal structure is detected as a main phase. Ina case where only a single structure is detected by the X-raydiffraction analysis, this detected structure is set as a main phase.The hexagonal ferrite type crystal structure includes at least an ironatom, a divalent metal atom, and an oxygen atom as constituting atoms. Adivalent metal atom is a metal atom which can be divalent cations asions, and examples thereof include an alkali earth metal atom such as astrontium atom, a barium atom, or a calcium atom, and a lead atom. Inthe invention and the specification, the hexagonal strontium ferritepowder is powder in which a main divalent metal atom included in thispowder is a strontium atom, and the hexagonal barium ferrite powder is apowder in which a main divalent metal atom included in this powder is abarium atom. The main divalent metal atom is a divalent metal atomoccupying the greatest content in the divalent metal atom included inthe powder based on atom %. However, the divalent metal atom describedabove does not include rare earth atom. The “rare earth atom” of theinvention and the specification is selected from the group consisting ofa scandium atom (Sc), an yttrium atom (Y), and a lanthanoid atom. Thelanthanoid atom is selected from the group consisting of a lanthanumatom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymiumatom (Nd), a promethium atom (Pm), a samarium atom (Sm), an europiumatom (Eu), a gadolinium atom (Gd), a terbium atom (Tb), a dysprosiumatom (Dy), a holmium atom (Ho), an erbium atom (Er), a thulium atom(Tm), an ytterbium atom (Yb), and a lutetium atom (Lu).

Hereinafter, the hexagonal strontium ferrite powder which is one aspectof the hexagonal ferrite powder will be described more specifically.

An activation volume of the hexagonal strontium ferrite powder ispreferably in a range of 800 to 1,600 nm³. The atomized hexagonalstrontium ferrite powder showing the activation volume in the rangedescribed above is suitable for manufacturing a magnetic tape exhibitingexcellent electromagnetic conversion characteristics. The activationvolume of the hexagonal strontium ferrite powder is preferably equal toor greater than 800 nm³, and can also be, for example, equal to orgreater than 850 nm³. In addition, from a viewpoint of further improvingthe electromagnetic conversion characteristics, the activation volume ofthe hexagonal strontium ferrite powder is more preferably equal to orsmaller than 1,500 nm³, even more preferably equal to or smaller than1,400 nm³, still preferably equal to or smaller than 1,300 nm³, stillmore preferably equal to or smaller than 1,200 nm³, and still even morepreferably equal to or smaller than 1,100 nm³. The same applies to theactivation volume of the hexagonal barium ferrite powder.

The “activation volume” is a unit of magnetization reversal and an indexshowing a magnetic magnitude of the particles. Regarding the activationvolume and an anisotropy constant Ku which will be described laterdisclosed in the invention and the specification, magnetic field sweeprates of a coercivity Hc measurement part at time points of 3 minutesand 30 minutes are measured by using an oscillation sample typemagnetic-flux meter (measurement temperature: 23° C.±1° C.), and theactivation volume and the anisotropy constant Ku are values acquiredfrom the following relational expression of Hc and an activation volumeV. A unit of the anisotropy constant Ku is 1 erg/cc=1.0×10⁻¹ J/m³.

Hc=2Ku/Ms{1−[(kT/KuV)ln(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant (unit: J/m³), Ms: saturationmagnetization (unit: kA/m), k: Boltzmann's constant, T: absolutetemperature (unit: K), V: activation volume (unit: cm³), A: spinprecession frequency (unit: s⁻¹), and t: magnetic field reversal time(unit: s)]

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Thehexagonal strontium ferrite powder can preferably have Ku equal to orgreater than 1.8×10⁵ J/m³, and more preferably have Ku equal to orgreater than 2.0×10⁵ J/m³. In addition, Ku of the hexagonal strontiumferrite powder can be, for example, equal to or smaller than 2.5×10⁵J/m³. However, the high Ku is preferable, because it means high thermalstability, and thus, Ku is not limited to the exemplified value.

The hexagonal strontium ferrite powder may or may not include the rareearth atom. In a case where the hexagonal strontium ferrite powderincludes the rare earth atom, a content (bulk content) of the rare earthatom is preferably 0.5 to 5.0 atom % with respect to 100 atom % of theiron atom. In one embodiment, the hexagonal strontium ferrite powderincluding the rare earth atom can have a rare earth atom surface layerportion uneven distribution. The “rare earth atom surface layer portionuneven distribution” of the invention and the specification means that acontent of rare earth atom with respect to 100 atom % of iron atom in asolution obtained by partially dissolving the hexagonal strontiumferrite powder with acid (hereinafter, referred to as a “rare earth atomsurface layer portion content” or simply a “surface layer portioncontent” regarding the rare earth atom) and a content of rare earth atomwith respect to 100 atom % of iron atom in a solution obtained bytotally dissolving the hexagonal strontium ferrite powder with acid(hereinafter, referred to as a “rare earth atom bulk content” or simplya “bulk content” regarding the rare earth atom) satisfy a ratio of rareearth atom surface layer portion content/rare earth atom bulk content>1.0.

The content of rare earth atom of the hexagonal strontium ferrite powderwhich will be described later is identical to the rare earth atom bulkcontent. With respect to this, the partial dissolving using acid is todissolve the surface layer portion of particles configuring thehexagonal strontium ferrite powder, and accordingly, the content of rareearth atom in the solution obtained by the partial dissolving is thecontent of rare earth atom in the surface layer portion of the particlesconfiguring the hexagonal strontium ferrite powder. The rare earth atomsurface layer portion content satisfying a ratio of “rare earth atomsurface layer portion content/rare earth atom bulk content >1.0” meansthat the rare earth atoms are unevenly distributed in the surface layerportion (that is, a larger amount of the rare earth atoms is present,compared to that inside), among the particles configuring the hexagonalstrontium ferrite powder. The surface layer portion of the invention andthe specification means a part of the region of the particlesconfiguring the hexagonal strontium ferrite powder towards the insidefrom the surface.

In a case where the hexagonal strontium ferrite powder includes the rareearth atom, a content (bulk content) of the rare earth atom ispreferably in a range of 0.5 to 5.0 atom % with respect to 100 atom % ofthe iron atom. It is thought that the rare earth atom having the bulkcontent in the range described above and uneven distribution of the rareearth atom in the surface layer portion of the particles configuring thehexagonal strontium ferrite powder contribute to the prevention of adecrease in reproducing output during the repeated reproducing. It issurmised that this is because the rare earth atom having the bulkcontent in the range described above included in the hexagonal strontiumferrite powder and the uneven distribution of the rare earth atom in thesurface layer portion of the particles configuring the hexagonalstrontium ferrite powder can increase the anisotropy constant Ku. As thevalue of the anisotropy constant Ku is high, occurrence of a phenomenoncalled thermal fluctuation (that is, improvement of thermal stability)can be prevented. By preventing the occurrence of the thermalfluctuation, a decrease in reproducing output during the repeatedreproducing can be prevented. It is surmised that the unevendistribution of the rare earth atom in the surface layer portion of theparticles of the hexagonal strontium ferrite powder contributes tostabilization of a spin at an iron (Fe) site in a crystal lattice of thesurface layer portion, thereby increasing the anisotropy constant Ku.

In addition, it is surmised that the use of the hexagonal strontiumferrite powder having the rare earth atom surface layer portion unevendistribution as the ferromagnetic powder of the magnetic layer alsocontributes to the prevention of chipping of the surface of the magneticlayer due to the sliding with the magnetic head. That is, it is surmisedthat, the hexagonal strontium ferrite powder having the rare earth atomsurface layer portion uneven distribution can also contribute to theimprovement of running durability of the magnetic tape. It is surmisedthat this is because the uneven distribution of the rare earth atom onthe surface of the particles configuring the hexagonal strontium ferritepowder contributes to improvement of an interaction between the surfaceof the particles and an organic substance (for example, binding agentand/or additive) included in the magnetic layer, thereby improvinghardness of the magnetic layer.

From a viewpoint of preventing reduction of the reproduction output inthe repeated reproduction and/or a viewpoint of further improvingrunning durability, the content of rare earth atom (bulk content) ismore preferably in a range of 0.5 to 4.5 atom %, even more preferably ina range of 1.0 to 4.5 atom %, and still preferably in a range of 1.5 to4.5 atom %.

The bulk content is a content obtained by totally dissolving thehexagonal strontium ferrite powder. In the invention and thespecification, the content of the atom is a bulk content obtained bytotally dissolving the hexagonal strontium ferrite powder, unlessotherwise noted. The hexagonal strontium ferrite powder including therare earth atom may include only one kind of rare earth atom or mayinclude two or more kinds of rare earth atom, as the rare earth atom. Ina case where two or more kinds of rare earth atoms are included, thebulk content is obtained from the total of the two or more kinds of rareearth atoms. The same also applies to the other components of theinvention and the specification. That is, for a given component, onlyone kind may be used or two or more kinds may be used, unless otherwisenoted. In a case where two or more kinds are used, the content is acontent of the total of the two or more kinds.

In a case where the hexagonal strontium ferrite powder includes the rareearth atom, the rare earth atom included therein may be any one or morekinds of the rare earth atom. Examples of the rare earth atom preferablefrom a viewpoint of preventing reduction of the reproduction outputduring the repeated reproduction include a neodymium atom, a samariumatom, an yttrium atom, and a dysprosium atom, a neodymium atom, asamarium atom, an yttrium atom are more preferable, and a neodymium atomis even more preferable.

In the hexagonal strontium ferrite powder having the rare earth atomsurface layer portion uneven distribution, a degree of unevendistribution of the rare earth atom is not limited, as long as the rareearth atom is unevenly distributed in the surface layer portion of theparticles configuring the hexagonal strontium ferrite powder. Forexample, regarding the hexagonal strontium ferrite powder having therare earth atom surface layer portion uneven distribution, a ratio ofthe surface layer portion content of the rare earth atom obtained bypartial dissolving performed under the dissolving conditions which willbe described later and the bulk content of the rare earth atom obtainedby total dissolving performed under the dissolving conditions which willbe described later, “surface layer portion content/bulk content” isgreater than 1.0 and can be equal to or greater than 1.5. The “surfacelayer portion content/bulk content” greater than 1.0 means that the rareearth atoms are unevenly distributed in the surface layer portion (thatis, a larger amount of the rare earth atoms is present, compared to thatinside), in the particles configuring the hexagonal strontium ferritepowder. A ratio of the surface layer portion content of the rare earthatom obtained by partial dissolving performed under the dissolvingconditions which will be described later and the bulk content of therare earth atom obtained by total dissolving performed under thedissolving conditions which will be described later, “surface layerportion content/bulk content” can be, for example, equal to or smallerthan 10.0, equal to or smaller than 9.0, equal to or smaller than 8.0,equal to or smaller than 7.0, equal to or smaller than 6.0, equal to orsmaller than 5.0, or equal to or smaller than 4.0. However, in thehexagonal strontium ferrite powder having the rare earth atom surfacelayer portion uneven distribution, the “surface layer portioncontent/bulk content” is not limited to the exemplified upper limit orthe lower limit, as long as the rare earth atom is unevenly distributedin the surface layer portion of the particles configuring the hexagonalstrontium ferrite powder.

The partial dissolving and the total dissolving of the hexagonalstrontium ferrite powder will be described below. Regarding thehexagonal strontium ferrite powder present as the powder, sample powderfor the partial dissolving and the total dissolving are collected frompowder of the same batch. Meanwhile, regarding the hexagonal strontiumferrite powder included in a magnetic layer of a magnetic tape, a partof the hexagonal strontium ferrite powder extracted from the magneticlayer is subjected to the partial dissolving and the other part issubjected to the total dissolving. The extraction of the hexagonalstrontium ferrite powder from the magnetic layer can be performed by,for example, a method disclosed in a paragraph 0032 of JP2015-91747A.

The partial dissolving means dissolving performed so that the hexagonalstrontium ferrite powder remaining in the solution can be visuallyconfirmed in a case of the completion of the dissolving. For example, byperforming the partial dissolving, a region of the particles configuringthe hexagonal strontium ferrite powder which is 10% to 20% by mass withrespect to 100% by mass of a total of the particles can be dissolved. Onthe other hand, the total dissolving means dissolving performed untilthe hexagonal strontium ferrite powder remaining in the solution is notvisually confirmed in a case of the completion of the dissolving.

The partial dissolving and the measurement of the surface layer portioncontent are, for example, performed by the following method. However,dissolving conditions such as the amount of sample powder and the likedescribed below are merely examples, and dissolving conditions capableof performing the partial dissolving and the total dissolving can berandomly used.

A vessel (for example, beaker) containing 12 mg of sample powder and 10mL of hydrochloric acid having a concentration of 1 mol/L is held on ahot plate at a set temperature of 70° C. for 1 hour. The obtainedsolution is filtered with a membrane filter having a hole diameter of0.1 μm. The element analysis of the filtrate obtained as described aboveis performed by an inductively coupled plasma (ICP) analysis device. Bydoing so, the surface layer portion content of the rare earth atom withrespect to 100 atom % of the iron atom can be obtained. In a case wherea plurality of kinds of rare earth atoms are detected from the elementanalysis, a total content of the entirety of the rare earth atoms is thesurface layer portion content. The same applies to the measurement ofthe bulk content.

Meanwhile, the total dissolving and the measurement of the bulk contentare, for example, performed by the following method.

A vessel (for example, beaker) containing 12 mg of sample powder and 10mL of hydrochloric acid having a concentration of 4 mol/L is held on ahot plate at a set temperature of 80° C. for 3 hours. After that, theprocess is performed in the same manner as in the partial dissolving andthe measurement of the surface layer portion content, and the bulkcontent with respect to 100 atom % of the iron atom can be obtained.

From a viewpoint of increasing reproducing output in a case ofreproducing data recorded on a magnetic tape, it is desirable that themass magnetization σs of ferromagnetic powder contained in the magnetictape is high. In regards to this point, in hexagonal strontium ferritepowder which includes the rare earth atom but does not have the rareearth atom surface layer portion uneven distribution, σs tends tosignificantly decrease, compared to that in hexagonal strontium ferritepowder not including the rare earth atom. With respect to this, it isthought that, hexagonal strontium ferrite powder having the rare earthatom surface layer portion uneven distribution is also preferable forpreventing such a significant decrease in σs. In one embodiment, σs ofthe hexagonal strontium ferrite powder can be equal to or greater than45 A×m²/kg and can also be equal to or greater than 47 A×m²/kg. On theother hand, from a viewpoint of noise reduction, σs is preferably equalto or smaller than 80 A×m²/kg and more preferably equal to or smallerthan 60 A×m²/kg. σs can be measured by using a well-known measurementdevice capable of measuring magnetic properties such as an oscillationsample type magnetic-flux meter. In the invention and the specification,the mass magnetization σs is a value measured at a magnetic fieldstrength of 15 kOe, unless otherwise noted. 1 [kOe]=(10⁶/4π) [A/m]

Regarding the content (bulk content) of the constituting atom in thehexagonal strontium ferrite powder, a content of the strontium atom canbe, for example, in a range of 2.0 to 15.0 atom % with respect to 100atom % of the iron atom. In one embodiment, in the hexagonal strontiumferrite powder, the divalent metal atom included in this powder can beonly a strontium atom. In another embodiment, the hexagonal strontiumferrite powder can also include one or more kinds of other divalentmetal atoms, in addition to the strontium atom. For example, thehexagonal strontium ferrite powder can include a barium atom and/or acalcium atom. In a case where the other divalent metal atom other thanthe strontium atom is included, a content of a barium atom and a contentof a calcium atom in the hexagonal strontium ferrite powder respectivelycan be, for example, in a range of 0.05 to 5.0 atom % with respect to100 atom % of the iron atom.

As the crystal structure of the hexagonal ferrite, a magnetoplumbitetype (also referred to as an “M type”), a W type, a Y type, and a Z typeare known. The hexagonal strontium ferrite powder may have any crystalstructure. The crystal structure can be confirmed by X-ray diffractionanalysis. In the hexagonal strontium ferrite powder, a single crystalstructure or two or more kinds of crystal structure can be detected bythe X-ray diffraction analysis. For example, In one embodiment, in thehexagonal strontium ferrite powder, only the M type crystal structurecan be detected by the X-ray diffraction analysis. For example, the Mtype hexagonal ferrite is represented by a compositional formula ofAFe₁₂O₁₉. Here, A represents a divalent metal atom, in a case where thehexagonal strontium ferrite powder has the M type, A is only a strontiumatom (Sr), or in a case where a plurality of divalent metal atoms areincluded as A, the strontium atom (Sr) occupies the hexagonal strontiumferrite powder with the greatest content based on atom % as describedabove. A content of the divalent metal atom in the hexagonal strontiumferrite powder is generally determined according to the type of thecrystal structure of the hexagonal ferrite and is not particularlylimited. The same applies to a content of an iron atom and a content ofan oxygen atom. The hexagonal strontium ferrite powder at least includesan iron atom, a strontium atom, and an oxygen atom, and can also includea rare earth atom. In addition, the hexagonal strontium ferrite powdermay or may not include atoms other than these atoms. As an example, thehexagonal strontium ferrite powder may include an aluminum atom (Al). Acontent of the aluminum atom can be, for example, 0.5 to 10.0 atom %with respect to 100 atom % of the iron atom. From a viewpoint ofpreventing the reduction of the reproduction output during the repeatedreproduction, the hexagonal strontium ferrite powder includes the ironatom, the strontium atom, the oxygen atom, and the rare earth atom, anda content of the atoms other than these atoms is preferably equal to orsmaller than 10.0 atom %, more preferably in a range of 0 to 5.0 atom %,and may be 0 atom % with respect to 100 atom % of the iron atom. Thatis, In one embodiment, the hexagonal strontium ferrite powder may notinclude atoms other than the iron atom, the strontium atom, the oxygenatom, and the rare earth atom. The content shown with atom % describedabove is obtained by converting a value of the content (unit: % by mass)of each atom obtained by totally dissolving the hexagonal strontiumferrite powder into a value shown as atom % by using the atomic weightof each atom. In addition, in the invention and the specification, agiven atom which is “not included” means that the content thereofobtained by performing total dissolving and measurement by using an ICPanalysis device is 0% by mass. A detection limit of the ICP analysisdevice is generally equal to or smaller than 0.01 ppm (parts permillion) based on mass. The expression “not included” is used as ameaning including that a given atom is included with the amount smallerthan the detection limit of the ICP analysis device. In one embodiment,the hexagonal strontium ferrite powder does not include a bismuth atom(Bi).

Metal Powder

As a preferred specific example of the ferromagnetic powder, aferromagnetic metal powder can also be used. For details of theferromagnetic metal powder, descriptions disclosed in paragraphs 0137 to0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A canbe referred to, for example.

ε-Iron Oxide Powder

As a preferred specific example of the ferromagnetic powder, an ε-ironoxide powder can also be used. In the invention and the specification,the “ε-iron oxide powder” is a ferromagnetic powder in which an ε-ironoxide type crystal structure is detected as a main phase by X-raydiffraction analysis. For example, in a case where the diffraction peakat the highest intensity in the X-ray diffraction spectrum obtained bythe X-ray diffraction analysis belongs to an ε-iron oxide type crystalstructure, it is determined that the ε-iron oxide type crystal structureis detected as a main phase. As a manufacturing method of the ε-ironoxide powder, a manufacturing method from a goethite, a reverse micellemethod, and the like are known. All of the manufacturing methods arewell known. For the method of manufacturing the ε-iron oxide powder inwhich a part of Fe is substituted with substitutional atoms such as Ga,Co, Ti, Al, or Rh, a description disclosed in J. Jpn. Soc. PowderMetallurgy Vol. 61 Supplement, No. 51, pp. S280-S284, J. Mater. Chem. C,2013, 1, pp. 5200-5206 can be referred, for example. However, themanufacturing method of the ε-iron oxide powder capable of being used asthe ferromagnetic powder in the magnetic layer of the magnetic tape isnot limited to the method described here.

An activation volume of the ε-iron oxide powder is preferably in a rangeof 300 to 1,500 nm³. The atomized ε-iron oxide powder showing theactivation volume in the range described above is suitable formanufacturing a magnetic tape exhibiting excellent electromagneticconversion characteristics. The activation volume of the ε-iron oxidepowder is preferably equal to or greater than 300 nm³, and can also be,for example, equal to or greater than 500 nm³. In addition, from aviewpoint of further improving the electromagnetic conversioncharacteristics, the activation volume of the ε-iron oxide powder ismore preferably equal to or smaller than 1,400 nm³, even more preferablyequal to or smaller than 1,300 nm³, still preferably equal to or smallerthan 1,200 nm³, and still more preferably equal to or smaller than 1,100nm³.

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Theε-iron oxide powder can preferably have Ku equal to or greater than3.0×10⁴ J/m³, and more preferably have Ku equal to or greater than8.0×10⁴ J/m³. In addition, Ku of the ε-iron oxide powder can be, forexample, equal to or smaller than 3.0×10⁵ J/m³. However, the high Ku ispreferable, because it means high thermal stability, and thus, Ku is notlimited to the exemplified value.

From a viewpoint of increasing reproducing output in a case ofreproducing data recorded on a magnetic tape, it is desirable that themass magnetization σs of ferromagnetic powder contained in the magnetictape is high. In regard to this point, in one embodiment, σs of theε-iron oxide powder can be equal to or greater than 8 A×m²/kg and canalso be equal to or greater than 12 A×m²/kg. On the other hand, from aviewpoint of noise reduction, σs of the ε-iron oxide powder ispreferably equal to or smaller than 40 A×m²/kg and more preferably equalto or smaller than 35 A×m²/kg.

In the invention and the specification, average particle sizes ofvarious powder such as the ferromagnetic powder and the like are valuesmeasured by the following method with a transmission electronmicroscope, unless otherwise noted.

The powder is imaged at an imaging magnification ratio of 100,000 with atransmission electron microscope, the image is printed on photographicprinting paper or displayed on a display so that the total magnificationratio of 500,000 to obtain an image of particles configuring the powder.A target particle is selected from the obtained image of particles, anoutline of the particle is traced with a digitizer, and a size of theparticle (primary particle) is measured. The primary particle is anindependent particle which is not aggregated.

The measurement described above is performed regarding 500 particlesarbitrarily extracted. An arithmetic average of the particle size of 500particles obtained as described above is the average particle size ofthe powder. As the transmission electron microscope, a transmissionelectron microscope H-9000 manufactured by Hitachi, Ltd. can be used,for example. In addition, the measurement of the particle size can beperformed by a well-known image analysis software, for example, imageanalysis software KS-400 manufactured by Carl Zeiss. The averageparticle size shown in examples which will be described later is a valuemeasured by using transmission electron microscope H-9000 manufacturedby Hitachi, Ltd. as the transmission electron microscope, and imageanalysis software KS-400 manufactured by Carl Zeiss as the imageanalysis software, unless otherwise noted. In the invention and thespecification, the powder means an aggregate of a plurality ofparticles. For example, the ferromagnetic powder means an aggregate of aplurality of ferromagnetic particles. The aggregate of the plurality ofparticles not only includes an embodiment in which particles configuringthe aggregate are directly in contact with each other, but also includesan embodiment in which a binding agent or an additive which will bedescribed later is interposed between the particles. A term, particlesmay be used for representing the powder.

As a method for collecting a sample powder from the magnetic tape inorder to measure the particle size, a method disclosed in a paragraph of0015 of JP2011-048878A can be used, for example.

In the invention and the specification, unless otherwise noted,

-   -   (1) in a case where the shape of the particle observed in the        particle image described above is a needle shape, a fusiform        shape, or a columnar shape (here, a height is greater than a        maximum long diameter of a bottom surface), the size (particle        size) of the particles configuring the powder is shown as a        length of a major axis configuring the particle, that is, a        major axis length,    -   (2) in a case where the shape of the particle is a planar shape        or a columnar shape (here, a thickness or a height is smaller        than a maximum long diameter of a plate surface or a bottom        surface), the particle size is shown as a maximum long diameter        of the plate surface or the bottom surface, and    -   (3) in a case where the shape of the particle is a sphere shape,        a polyhedron shape, or an unspecified shape, and the major axis        configuring the particles cannot be specified from the shape,        the particle size is shown as an equivalent circle diameter. The        equivalent circle diameter is a value obtained by a circle        projection method.

In addition, regarding an average acicular ratio of the powder, a lengthof a minor axis, that is, a minor axis length of the particles ismeasured in the measurement described above, a value of (major axislength/minor axis length) of each particle is obtained, and anarithmetic average of the values obtained regarding 500 particles iscalculated. Here, unless otherwise noted, in a case of (1), the minoraxis length as the definition of the particle size is a length of aminor axis configuring the particle, in a case of (2), the minor axislength is a thickness or a height, and in a case of (3), the major axisand the minor axis are not distinguished, thus, the value of (major axislength/minor axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of theparticle is specified, for example, in a case of definition of theparticle size (1), the average particle size is an average major axislength, and in a case of the definition (2), the average particle sizeis an average plate diameter. In a case of the definition (3), theaverage particle size is an average diameter (also referred to as anaverage particle diameter).

The content (filling percentage) of the ferromagnetic powder of themagnetic layer is preferably in a range of 50% to 90% by mass and morepreferably in a range of 60% to 90% by mass with respect to a total massof the magnetic layer. A high filling percentage of the ferromagneticpowder in the magnetic layer is preferable from a viewpoint ofimprovement of recording density.

Binding Agent

The magnetic tape may be a coating type magnetic tape, and can include abinding agent in the magnetic layer. The binding agent is one or morekinds of resin. As the binding agent, various resins normally used as abinding agent of a coating type magnetic recording medium can be used.As the binding agent, a resin selected from a polyurethane resin, apolyester resin, a polyamide resin, a vinyl chloride resin, an acrylicresin obtained by copolymerizing styrene, acrylonitrile, or methylmethacrylate, a cellulose resin such as nitrocellulose, an epoxy resin,a phenoxy resin, and a polyvinylalkylal resin such as polyvinyl acetalor polyvinyl butyral can be used alone or a plurality of resins can bemixed with each other to be used. Among these, a polyurethane resin, anacrylic resin, a cellulose resin, and a vinyl chloride resin arepreferable. These resins may be a homopolymer or a copolymer. Theseresins can be used as the binding agent even in the non-magnetic layerand/or a back coating layer which will be described later. For thebinding agent described above, descriptions disclosed in paragraphs 0028to 0031 of JP2010-24113A can be referred to. In addition, the bindingagent may be a radiation curable resin such as an electron beam curableresin. For the radiation curable resin, paragraphs 0044 and 0045 ofJP2011-048878A can be referred to.

An average molecular weight of the resin used as the binding agent canbe, for example, 10,000 to 200,000 as a weight-average molecular weight.The weight-average molecular weight of the invention and thespecification is a value obtained by performing polystyrene conversionof a value measured by gel permeation chromatography (GPC) under thefollowing measurement conditions. The weight-average molecular weight ofthe binding agent shown in examples which will be described later is avalue obtained by performing polystyrene conversion of a value measuredunder the following measurement conditions. The amount of the bindingagent used can be, for example, 1.0 to 30.0 parts by mass with respectto 100.0 parts by mass of the ferromagnetic powder.

GPC device: HLC-8120 (manufactured by Tosoh Corporation)

Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mmID (inner diameter)×30.0 cm)

Eluent: Tetrahydrofuran (THF)

Curing Agent

A curing agent can also be used together with the binding agent. As thecuring agent, In one embodiment, a thermosetting compound which is acompound in which a curing reaction (crosslinking reaction) proceeds dueto heating can be used, and in another embodiment, a photocurablecompound in which a curing reaction (crosslinking reaction) proceeds dueto light irradiation can be used. At least a part of the curing agent isincluded in the magnetic layer in a state of being reacted (crosslinked)with other components such as the binding agent, by proceeding thecuring reaction in the manufacturing step of the magnetic tape. Thepreferred curing agent is a thermosetting compound, and polyisocyanateis suitable. For the details of polyisocyanate, descriptions disclosedin paragraphs 0124 and 0125 of JP2011-216149A can be referred to. Theamount of the curing agent can be, for example, 0 to 80.0 parts by masswith respect to 100.0 parts by mass of the binding agent in the magneticlayer forming composition, and is preferably 50.0 to 80.0 parts by mass,from a viewpoint of improvement of hardness of each layer such as themagnetic layer.

Additives

The magnetic layer may include one or more kinds of additives, asnecessary. As the additives, the curing agent described above is used asan example. In addition, examples of the additive included in themagnetic layer include a non-magnetic powder (for example, inorganicpowder, carbon black, or the like), a lubricant, a dispersing agent, adispersing assistant, a fungicide, an antistatic agent, and anantioxidant. For the lubricant, a description disclosed in paragraphs0030 to 0033, 0035, and 0036 of JP2016-126817A can be referred to. Thelubricant may be included in the non-magnetic layer which will bedescribed later. For the lubricant which can be included in thenon-magnetic layer, a description disclosed in paragraphs 0030, 0031,0034 to 0036 of JP2016-126817A can be referred to. For the dispersingagent, a description disclosed in paragraphs 0061 and 0071 ofJP2012-133837A can be referred to. The dispersing agent may be added toa non-magnetic layer forming composition. For the dispersing agent whichcan be added to the non-magnetic layer forming composition, adescription disclosed in paragraph 0061 of JP2012-133837A can bereferred to. As the non-magnetic powder which may be contained in themagnetic layer, non-magnetic powder which can function as an abrasive,non-magnetic powder (for example, non-magnetic colloid particles) whichcan function as a projection formation agent which forms projectionssuitably protruded from the surface of the magnetic layer, and the likecan be used. An average particle size of colloidal silica (silicacolloid particles) shown in the examples which will be described lateris a value obtained by a method disclosed in a measurement method of anaverage particle diameter in a paragraph 0015 of JP2011-048878A. As theadditives, a commercially available product can be suitably selectedaccording to the desired properties or manufactured by a well-knownmethod, and can be used with any amount. As an example of the additivewhich can be used for improving dispersibility of the abrasive in themagnetic layer including the abrasive, a dispersing agent disclosed inparagraphs 0012 to 0022 of JP2013-131285A can be used.

The magnetic layer described above can be provided on the surface of thenon-magnetic support directly or indirectly through the non-magneticlayer.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape mayinclude a magnetic layer directly on the non-magnetic support or mayinclude a non-magnetic layer containing the non-magnetic powder betweenthe non-magnetic support and the magnetic layer. The non-magnetic powderused for the non-magnetic layer may be a powder of an inorganicsubstance (inorganic powder) or a powder of an organic substance(organic powder). In addition, carbon black and the like can be used.Examples of the inorganic substance include metal, metal oxide, metalcarbonate, metal sulfate, metal nitride, metal carbide, and metalsulfide. The non-magnetic powder can be purchased as a commerciallyavailable product or can be manufactured by a well-known method. Fordetails thereof, descriptions disclosed in paragraphs 0146 to 0150 ofJP2011-216149A can be referred to. For carbon black capable of beingused in the non-magnetic layer, a description disclosed in paragraphs0040 and 0041 of JP2010-24113A can be referred to. The content (fillingpercentage) of the non-magnetic powder of the non-magnetic layer ispreferably in a range of 50% to 90% by mass and more preferably in arange of 60% to 90% by mass with respect to a total mass of thenon-magnetic layer.

In one embodiment, the non-magnetic layer can contain a Fe-basedinorganic oxide powder as the non-magnetic powder. In the invention andthe specification, the “Fe-based inorganic oxide powder” refers to aninorganic oxide powder containing iron as a constituent element.Specific examples of the Fe-based inorganic oxide powder can include anα-iron oxide powder and a goethite powder. In the invention and thespecification, the “α-iron oxide powder” is a non-magnetic powder inwhich an α-iron oxide type crystal structure is detected as a main phaseby X-ray diffraction analysis. The α-iron oxide powder is also generallycalled hematite or the like.

According to the studies of the present inventors regarding thenon-magnetic layer, it is found that the non-magnetic layer containingthe Fe-based inorganic oxide powder having an average particle volume of2.0×10⁻⁶ μm³ tends to have high hardness. The present inventors considerthat this point is preferable for stably performing a burnishing processwhich will be described later. The present inventors surmise that, in acase where the burnishing process is stably performed, the edge portionRa and the central portion Ra can be easily controlled, and as a result,the Ra ratio can be easily controlled. From this point, the averageparticle volume of the Fe-based inorganic oxide powder contained in thenon-magnetic layer is preferably 2.0×10⁻⁶ μm³ or less, more preferably1.5×10⁻⁶ μm³ or less, and even more preferably 1.0×10⁻⁶ μm³ or less. Theaverage particle volume can be, for example, 1.0×10⁻⁹ μm³ or more or1.0×10⁻⁸ μm³ or more, or can be less than the value exemplified here.

In the invention and the specification, the average particle volume is avalue obtained by the following method.

In order to observe the Fe-based inorganic oxide powder contained in thenon-magnetic layer of the magnetic tape, first, as a samplepretreatment, flaking is performed by a microtome method. The flaking isperformed so that a flaky sample capable of observing a cross section ofthe magnetic tape in the thickness direction is obtained along thelongitudinal direction of the magnetic tape. In the examples which willbe described later, Leica EM UC6 manufactured by Leica was used as amicrotome in order to obtain the average particle volume of the Fe-basedinorganic oxide powder.

For the obtained flaky sample, a cross section observation is performedso as to include a range from the non-magnetic support to the magneticlayer, using a transmission electron microscope (TEM) at an accelerationvoltage of 300 kV and a to magnetic layer of 200,000 times, and across-sectional TEM image is obtained. As the transmission electronmicroscope, for example, JEM-2100Plus manufactured by JEOL Ltd. can beused. For the examples which will be described later, JEM-2100Plusmanufactured by JEOL Ltd. was used as a transmission electronmicroscope, in order to obtain the average particle volume of theFe-based inorganic oxide powder.

In the obtained cross-sectional TEM image, 50 particles of Fe-basedinorganic oxide powder are specified from the particles contained in thenon-magnetic layer by using a micro electron beam diffraction method.Electron beam diffraction by the micro electron beam diffraction methodis performed using a transmission electron microscope at an accelerationvoltage of 200 kV and a camera length of 50 cm. For the examples whichwill be described later, JEM-2100Plus manufactured by JEOL Ltd. was usedas the transmission electron microscope for the electron beamdiffraction by the micro electron beam diffraction method.

Then, using the 50 particles of the Fe-based inorganic oxide powderspecified as described above, the average particle volume is obtained asfollows.

First, a major axis length (hereinafter referred to as “DL”) and a minoraxis length (hereinafter referred to as “DS”) of each particle aremeasured.

The major axis length DL means a maximum distance among distancesbetween two parallel lines drawn from all angles so as to be in contactwith a contour of the particle (so-called maximum feret's diameter).

In a case where a direction of the major axis length defined asdescribed above is called a major axis direction, the minor axis lengthDS means a maximum length among lengths of the particle in a directionorthogonal to the major axis direction of the particle.

Next, an average major axis length DLave is obtained as an arithmeticaverage of the major axis lengths DL of the 50 measured particles. aveis an abbreviation for average.

In addition, an average minor axis length DSave is obtained as anarithmetic average of the minor axis lengths DS of the 50 particles.

From the average major axis length DLave and the average minor axislength DSave, an average volume Vave of the particles is obtained by thefollowing equation.

Vave=π/6×DSave² ×DLave

In addition, in one embodiment, the non-magnetic layer may containcarbon black as the non-magnetic powder. An average particle size ofcarbon black can be, for example, 10 nm to 50 nm. According to thestudies of the present inventors, it is found that the non-magneticlayer containing carbon black having a pH of 5.0 or less tends to havehigh hardness. The present inventors consider that this point ispreferable for stably performing a burnishing process which will bedescribed later. The present inventors surmise that, in a case where theburnishing process is stably performed, the edge portion Ra and thecentral portion Ra can be easily controlled, and as a result, the Raratio can be easily controlled. From this point, the pH of the carbonblack contained in the non-magnetic layer is preferably 5.0 or less, andmore preferably 4.0 or less. The pH can be, for example, 1.0 or more,2.0 or more, or 3.0 or more, or can be less than the value exemplifiedhere.

In the present invention and the present specification, the pH of carbonblack is a value measured according to the standard test method ASTMD1512.

The non-magnetic layer preferably contains at least one of the Fe-basedinorganic oxide powder having an average particle volume of 2.0×10⁻⁶ μm³or less and the carbon black having a pH of 5.0 or less, and morepreferably contains both of them. A content of Fe-based inorganic oxidepowder having an average particle volume of 2.0×10⁻⁶ μm³ or less withrespect to 100 parts by mass of the total non-magnetic powder containedin the non-magnetic layer can be 50 parts by mass or more, 60 parts bymass or more, or 70 parts by mass or more, and can be, for example, 90parts by mass or less. A content of carbon black having a pH of 5.0 orless with respect to 100 parts by mass of the total non-magnetic powdercontained in the non-magnetic layer can be 10 parts by mass or more or20 parts by mass or more, and can be, for example, 50 parts by mass orless, 40 parts by mass or less, or 30 parts by mass or less.

The non-magnetic layer can include a binding agent and can also includeadditives. In regards to other details of a binding agent or additivesof the non-magnetic layer, the well-known technology regarding thenon-magnetic layer can be applied. In addition, in regards to the typeand the content of the binding agent, and the type and the content ofthe additive, for example, the well-known technology regarding themagnetic layer can be applied.

The non-magnetic layer of the magnetic tape also includes asubstantially non-magnetic layer containing a small amount offerromagnetic powder as impurities, or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Non-Magnetic Support

Next, the non-magnetic support will be described. As the non-magneticsupport (hereinafter, also simply referred to as a “support”),well-known components such as polyethylene terephthalate, polyethylenenaphthalate, polyamide, polyamide imide, aromatic polyamide subjected tobiaxial stretching are used. Among these, polyethylene terephthalate,polyethylene naphthalate, and polyamide are preferable. Coronadischarge, plasma treatment, easy-bonding treatment, or heat treatmentmay be performed with respect to these supports in advance.

Back Coating Layer

The tape may or may not include a back coating layer including anon-magnetic powder on a surface side of the non-magnetic supportopposite to the surface side provided with the magnetic layer. The backcoating layer preferably includes any one or both of carbon black andinorganic powder. The back coating layer can include a binding agent andcan also include additives. For the details of the non-magnetic powder,the binding agent included in the back coating layer and variousadditives, a well-known technology regarding the back coating layer canbe applied, and a well-known technology regarding the magnetic layerand/or the non-magnetic layer can also be applied. For example, for theback coating layer, descriptions disclosed in paragraphs 0018 to 0020 ofJP2006-331625A and page 4, line 65, to page 5, line 38, of U.S. Pat. No.7,029,774B can be referred to.

Various Thicknesses

Regarding a thickness (total thickness) of the magnetic tape, it hasbeen required to increase recording capacity (increase in capacity) ofthe magnetic tape along with the enormous increase in amount ofinformation in recent years. As a unit for increasing the capacity, athickness of the magnetic tape is reduced and a length of the magnetictape accommodated in one reel of the magnetic tape cartridge isincreased. From this point, the thickness (total thickness) of themagnetic tape is preferably 5.6 μm or less, more preferably 5.5 μm orless, even more preferably 5.4 μm or less, still preferably 5.3 μm orless, and still more preferably 5.2 μm or less. In addition, from aviewpoint of ease of handling, the thickness of the magnetic tape ispreferably 3.0 μm or more and more preferably 3.5 μm or more.

The thickness (total thickness) of the magnetic tape can be measured bythe following method.

Ten tape samples (for example, length of 5 to 10 cm) are cut out from arandom portion of the magnetic tape, these tape samples are overlapped,and the thickness is measured. A value which is one tenth of themeasured thickness (thickness per one tape sample) is set as the tapethickness. The thickness measurement can be performed using a well-knownmeasurement device capable of performing the thickness measurement at0.1 μm order.

A thickness of the non-magnetic support is preferably 3.0 to 5.0 μm.

A thickness of the magnetic layer can be optimized according to asaturation magnetization amount of a magnetic head used, a head gaplength, a recording signal band, and the like, is normally 0.01 μm to0.15 μm, and is preferably 0.02 μm to 0.12 μm and more preferably 0.03μm to 0.1 μm, from a viewpoint of realization of high-density recording.The magnetic layer may be at least single layer, the magnetic layer maybe separated into two or more layers having different magneticproperties, and a configuration of a well-known multilayered magneticlayer can be applied. A thickness of the magnetic layer in a case wherethe magnetic layer is separated into two or more layers is the totalthickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm andis preferably 0.1 to 1.0 μm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.9 μm and more preferably 0.1 to 0.7 μm.

Various thicknesses such as the thickness of the magnetic layer and thelike can be obtained by the following method.

A cross section of the magnetic tape in the thickness direction isexposed with an ion beam and the cross section observation of theexposed cross section is performed using a scanning electron microscopeor a transmission electron microscope. Various thicknesses can beobtained as the arithmetic average of the thicknesses obtained at tworandom portions in the cross section observation. Alternatively, variousthicknesses can be obtained as a designed thickness calculated under themanufacturing conditions.

Manufacturing Method

Preparation of Each Layer Forming Composition

A step of preparing a composition for forming the magnetic layer, thenon-magnetic layer or the back coating layer can generally include atleast a kneading step, a dispersing step, and a mixing step providedbefore and after these steps, in a case where necessary. Each step maybe divided into two or more stages. The component used in thepreparation of each layer forming composition may be added at an initialstage or in a middle stage of each step. As the solvent, one kind or twoor more kinds of various kinds of solvents usually used for producing acoating type magnetic recording medium can be used. For the solvent, adescription disclosed in a paragraph 0153 of JP2011-216149A can bereferred to, for example. In addition, each component may be separatelyadded in two or more steps. For example, a binding agent may beseparately added in a kneading step, a dispersing step, and a mixingstep for adjusting viscosity after the dispersion. In order tomanufacture the magnetic tape, a well-known manufacturing technology canbe used in various steps. In the kneading step, an open kneader, acontinuous kneader, a pressure kneader, or a kneader having a strongkneading force such as an extruder is preferably used. For details ofthe kneading processes, descriptions disclosed in JP1989-106338A(JP-H01-106338A) and JP1989-79274A (JP-H01-79274A) can be referred to.As a disperser, a well-known dispersion device can be used. Thefiltering may be performed by a well-known method in any stage forpreparing each layer forming composition. The filtering can be performedby using a filter, for example. As the filter used in the filtering, afilter having a hole diameter of 0.01 to 3 μm (for example, filter madeof glass fiber or filter made of polypropylene) can be used, forexample.

Coating Step

The magnetic layer can be formed, for example, by directly applying themagnetic layer forming composition onto the non-magnetic support orperforming multilayer coating of the magnetic layer forming compositionwith the non-magnetic layer forming composition in order or at the sametime. In an case of performing an alignment process, while the coatinglayer of the magnetic layer forming composition is wet, the alignmentprocess is performed with respect to the coating layer in an alignmentzone. For the alignment process, various technologies disclosed in aparagraph 0052 of JP2010-24113A can be applied. For example, ahomeotropic alignment process can be performed by a well-known methodsuch as a method using a different polar facing magnet. In the alignmentzone, a drying speed of the coating layer can be controlled by atemperature and an air flow of the dry air and/or a transporting rate inthe alignment zone. In addition, the coating layer may be preliminarilydried before transporting to the alignment zone.

The back coating layer can be formed by applying a back coating layerforming composition onto a side of the non-magnetic support opposite tothe side provided with the magnetic layer (or to be provided with themagnetic layer).

For details of the coating for forming each layer, a descriptiondisclosed in a paragraph 0066 of JP2010-231843A can be referred to.

Other Steps

After performing the coating step described above, a calendar processcan usually be performed in order to improve surface smoothness of themagnetic tape. For calendar conditions, a calendar pressure is, forexample, 200 to 500 kN/m and preferably 250 to 350 kN/m, a calendartemperature is, for example, 70° C. to 120° C. and preferably 80° C. to100° C., and a calendar speed is, for example, 50 to 300 m/min andpreferably 80 to 200 m/min. In addition, as a roll having a hard surfaceis used as a calendar roll, or as the number of stages is increased, thesurface of the magnetic layer tends to be smoother.

For various other steps for manufacturing a magnetic tape, a descriptiondisclosed in paragraphs 0067 to 0070 of JP2010-231843A can be referredto.

Through various steps, a long magnetic tape raw material can beobtained. The obtained magnetic tape raw material is, for example, cut(slit) by a well-known cutter to have a width of a magnetic tape to beaccommodated in the magnetic tape cartridge. The width can be determinedaccording to the standard and is normally ½ inches. 1 inch=2.54 cm.

Burnishing Process

The burnishing process is a process of rubbing a surface of a processtarget with a member (for example, abrasive tape or a grinding tool suchas a blade for grinding or a wheel for grinding). The burnishing processcan be preferably performed by performing one or both of rubbing(polishing) of a surface of a coating layer which is a process targetwith an abrasive tape, and rubbing (grinding) of a surface of a coatinglayer which is a process target with a grinding tool. As the abrasivetape, a commercially available product may be used or an abrasive tapeproduced by a well-known method may be used. In addition, as thegrinding tool, a well-known blade for grinding such as a fixed typeblade, a diamond wheel, or a rotary blade, or a wheel for grinding canbe used. Further, a wiping process of wiping the surface of the coatinglayer rubbed with the abrasive tape and/or the grinding tool with awiping material may be performed. For details of the preferable abrasivetape, grinding tool, burnishing process, and wiping process, paragraphs0034 to 0048, FIG. 1 , and examples of JP1994-052544A (JP-H06-052544A)can be referred to. The roughness of the surface to be treated can becontrolled by the burnishing process, and as the burnishing processconditions are reinforced, the surface to be processed tends to besmooth. Examples of the burnishing process conditions include a tensionapplied in the longitudinal direction of the magnetic tape during theburnishing process (hereinafter, referred to as a “burnishing processtension”). The larger the value of the burnishing process tension, thesmoother the surface to be processed tends to be. In order to controleach of the edge portion Ra and the central portion Ra of the magneticlayer surface and to control the Ra ratio (central portion Ra/edgeportion Ra) accordingly, it is preferable to perform the burnishingprocess on a central region of the surface of the magnetic layer and theburnishing process on a region in the vicinity of each edge(hereinafter, referred to as the “region in the vicinity of the edge”)under different process conditions, in a case of performing theburnishing process on the surface of the magnetic layer of the magnetictape after the slitting. In the magnetic tape slit to a width of ½ inch,for example, the central region can be a region between the position ofthe inner side of 3 mm from the one edge and the position of the innerside of 3 mm from the other edge in the width direction of the magnetictape, and a region other than such a central region can be referred toas the region in the vicinity of the edge. The central region and theregion in the vicinity of the edge described with respect to theexamples which will be described later are the regions described above.

For example, by making a value of a burnishing process tension duringthe burnishing process on the central region larger than a value of aburnishing process tension during the burnishing process on the regionin the vicinity of the edge, the central region can be made smootherthan the region in the vicinity of the edge, and as a result, the valueof the edge portion Ra can be made larger than the value of the centralportion Ra. In both the burnishing process on the central region and theburnishing process on the region in the vicinity of the edge, theburnishing process tension can be in a range of, for example, 50 gf to250 gf, and a difference therebetween (the burnishing process tension inthe central region—the burnishing process tension in the region in thevicinity of the edge) can be, for example, 3 gf to 30 gf. However, therange described above is an example and does not limit the presentinvention. In terms of unit, “gf” represents gram weight and 1 N(Newton) is approximately 102 gf.

Formation of Servo Pattern

In the magnetic tape obtained by slitting, a servo pattern can begenerally formed. The formation of the servo pattern can be performed,for example, after the burnishing process described above (or even afterthe wiping process). The “formation of the servo pattern” can be“recording of a servo signal”. The formation of the servo pattern willbe described below.

The servo pattern is generally formed along a longitudinal direction ofthe magnetic tape. As a system of control using a servo signal (servocontrol), timing-based servo (TBS), amplitude servo, or frequency servois used.

As shown in European Computer Manufacturers Association (ECMA)-319 (June2001), a timing-based servo system is used in a magnetic tape based on alinear tape-open (LTO) standard (generally referred to as an “LTOtape”). In this timing-based servo system, the servo pattern isconfigured by continuously disposing a plurality of pairs of magneticstripes (also referred to as “servo stripes”) not parallel to each otherin a longitudinal direction of the magnetic tape. In the invention andthe specification, the “timing-based servo pattern” refers to a servopattern that enables head tracking in a servo system of a timing-basedservo system. As described above, a reason for that the servo pattern isconfigured with one pair of magnetic stripes not parallel to each otheris because a servo signal reading element passing on the servo patternrecognizes a passage position thereof. Specifically, one pair of themagnetic stripes are formed so that a gap thereof is continuouslychanged along the width direction of the magnetic tape, and a relativeposition of the servo pattern and the servo signal reading element canbe recognized, by the reading of the gap thereof by the servo signalreading element. The information of this relative position can realizethe tracking of a data track. Accordingly, a plurality of servo tracksare generally set on the servo pattern along the width direction of themagnetic tape.

The servo band is configured of servo patterns continuous in thelongitudinal direction of the magnetic tape. A plurality of servo bandsare normally provided on the magnetic tape. For example, the numberthereof is 5 in the LTO tape. A region interposed between two adjacentservo bands is a data band. The data band is configured of a pluralityof data tracks and each data track corresponds to each servo track.

In one embodiment, as shown in JP2004-318983A, information showing thenumber of servo band (also referred to as “servo band identification(ID)” or “Unique Data Band Identification Method (UDIM) information”) isembedded in each servo band. This servo band ID is recorded by shiftinga specific servo stripe among the plurality of pair of servo stripes inthe servo band so that the position thereof is relatively deviated inthe longitudinal direction of the magnetic tape. Specifically, theposition of the shifted specific servo stripe among the plurality ofpair of servo stripes is changed for each servo band. Accordingly, therecorded servo band ID becomes unique for each servo band, andtherefore, the servo band can be uniquely specified by only reading oneservo band by the servo signal reading element.

In a method of uniquely specifying the servo band, a staggered method asshown in ECMA-319 (June 2001) is used. In this staggered method, aplurality of the groups of one pair of magnetic stripes (servo stripe)not parallel to each other which are continuously disposed in thelongitudinal direction of the magnetic tape is recorded so as to beshifted in the longitudinal direction of the magnetic tape for eachservo band. A combination of this shifted servo band between theadjacent servo bands is set to be unique in the entire magnetic tape,and accordingly, the servo band can also be uniquely specified byreading of the servo pattern by two servo signal reading elements.

In addition, as shown in ECMA-319 (June 2001), information showing theposition in the longitudinal direction of the magnetic tape (alsoreferred to as “Longitudinal Position (LPOS) information”) is normallyembedded in each servo band. This LPOS information is recorded so thatthe position of one pair of servo stripes is shifted in the longitudinaldirection of the magnetic tape, in the same manner as the UDIMinformation. However, unlike the UDIM information, the same signal isrecorded on each servo band in this LPOS information.

Other information different from the UDIM information and the LPOSinformation can be embedded in the servo band. In this case, theembedded information may be different for each servo band as the UDIMinformation, or may be common in all of the servo bands, as the LPOSinformation.

In addition, as a method of embedding the information in the servo band,a method other than the method described above can be used. For example,a predetermined code may be recorded by thinning out a predeterminedpair among the group of pairs of the servo stripes.

A servo pattern forming head is also referred to as a servo write head.The servo write head generally includes pairs of gaps corresponding tothe pairs of magnetic stripes by the number of servo bands. In general,a core and a coil are respectively connected to each of the pairs ofgaps, and a magnetic field generated in the core can generate leakagemagnetic field in the pairs of gaps, by supplying a current pulse to thecoil. In a case of forming the servo pattern, by inputting a currentpulse while causing the magnetic tape to run on the servo write head,the magnetic pattern corresponding to the pair of gaps is transferred tothe magnetic tape, and the servo pattern can be formed. A width of eachgap can be suitably set in accordance with a density of the servopattern to be formed. The width of each gap can be set as, for example,equal to or smaller than 1 μm, 1 to 10 μm, or equal to or greater than10 μm.

Before forming the servo pattern on the magnetic tape, a demagnetization(erasing) process is generally performed on the magnetic tape. Thiserasing process can be performed by applying a uniform magnetic field tothe magnetic tape by using a DC magnet and an AC magnet. The erasingprocess includes direct current (DC) erasing and alternating current(AC) erasing. The AC erasing is performed by slowing decreasing anintensity of the magnetic field, while reversing a direction of themagnetic field applied to the magnetic tape. Meanwhile, the DC erasingis performed by applying the magnetic field in one direction to themagnetic tape. The DC erasing further includes two methods. A firstmethod is horizontal DC erasing of applying the magnetic field in onedirection along a longitudinal direction of the magnetic tape. A secondmethod is vertical DC erasing of applying the magnetic field in onedirection along a thickness direction of the magnetic tape. The erasingprocess may be performed with respect to all of the magnetic tape or maybe performed for each servo band of the magnetic tape.

A direction of the magnetic field to the servo pattern to be formed isdetermined in accordance with the direction of erasing. For example, ina case where the horizontal DC erasing is performed to the magnetictape, the formation of the servo pattern is performed so that thedirection of the magnetic field and the direction of erasing is oppositeto each other. Accordingly, the output of the servo signal obtained bythe reading of the servo pattern can be increased. As disclosed inJP2012-53940A, in a case where the magnetic pattern is transferred tothe magnetic tape subjected to the vertical DC erasing by using the gap,the servo signal obtained by the reading of the formed servo pattern hasa unipolar pulse shape. Meanwhile, in a case where the magnetic patternis transferred to the magnetic tape subjected to the horizontal DCerasing by using the gap, the servo signal obtained by the reading ofthe formed servo pattern has a bipolar pulse shape.

Heat Treatment

In one embodiment, the magnetic tape can be a magnetic tape manufacturedthrough the following heat treatment. In another aspect, the magnetictape can be manufactured without the following heat treatment.

The heat treatment can be performed in a state where the magnetic tapeslit and cut to have a width determined according to the standard iswound around a core member.

In one embodiment, the heat treatment is performed in a state where themagnetic tape is wound around the core member for heat treatment(hereinafter, referred to as a “core for heat treatment”), the magnetictape after the heat treatment is wound around a cartridge reel of themagnetic tape cartridge, and a magnetic tape cartridge in which themagnetic tape is wound around the cartridge reel can be manufactured.

The core for heat treatment can be formed of metal, a resin, or paper.The material of the core for heat treatment is preferably a materialhaving high stiffness, from a viewpoint of preventing the occurrence ofa winding defect such as spoking or the like. From this viewpoint, thecore for heat treatment is preferably formed of metal or a resin. Inaddition, as an index for stiffness, a bending elastic modulus of thematerial for the core for heat treatment is preferably equal to orgreater than 0.2 GPa (gigapascal) and more preferably equal to orgreater than 0.3 GPa. Meanwhile, since the material having highstiffness is normally expensive, the use of the core for heat treatmentof the material having stiffness exceeding the stiffness capable ofpreventing the occurrence of the winding defect causes the costincrease. By considering the viewpoint described above, the bendingelastic modulus of the material for the core for heat treatment ispreferably equal to or smaller than 250 GPa. The bending elastic modulusis a value measured based on international organization forstandardization (ISO) 178 and the bending elastic modulus of variousmaterials is well known. In addition, the core for heat treatment can bea solid or hollow core member. In a case of a hollow shape, a wallthickness is preferably equal to or greater than 2 mm, from a viewpointof maintaining the stiffness. In addition, the core for heat treatmentmay include or may not include a flange.

The magnetic tape having a length equal to or greater than a length tobe finally accommodated in the magnetic tape cartridge (hereinafter,referred to as a “final product length”) is prepared as the magnetictape wound around the core for heat treatment, and it is preferable toperform the heat treatment by placing the magnetic tape in the heattreatment environment, in a state where the magnetic tape is woundaround the core for heat treatment. The magnetic tape length woundaround the core for heat treatment is equal to or greater than the finalproduct length, and is preferably the “final product length+α”, from aviewpoint of ease of winding around the core for heat treatment. This ais preferably equal to or greater than 5 m, from a viewpoint of ease ofthe winding. The tension in a case of winding around the core for heattreatment is preferably equal to or greater than 0.1 N (newton). Inaddition, from a viewpoint of preventing the occurrence of excessivedeformation during the manufacturing, the tension in a case of windingaround the core for heat treatment is preferably equal to or smallerthan 1.5 N and more preferably equal to or smaller than 1.0 N. An outerdiameter of the core for heat treatment is preferably equal to orgreater than 20 mm and more preferably equal to or greater than 40 mm,from viewpoints of ease of the winding and preventing coiling (curl inlongitudinal direction). The outer diameter of the core for heattreatment is preferably equal to or smaller than 100 mm and morepreferably equal to or smaller than 90 mm. A width of the core for heattreatment may be equal to or greater than the width of the magnetic tapewound around this core. In addition, after the heat treatment, in a caseof detaching the magnetic tape from the core for heat treatment, it ispreferable that the magnetic tape and the core for heat treatment aresufficiently cooled and magnetic tape is detached from the core for heattreatment, in order to prevent the occurrence of the tape deformationwhich is not intended during the detaching operation. It is preferablethe detached magnetic tape is wound around another core temporarily(referred to as a “core for temporary winding”), and the magnetic tapeis wound around a cartridge reel (generally, outer diameter isapproximately 40 to 50 mm) of the magnetic tape cartridge from the corefor temporary winding. Accordingly, a relationship between the insideand the outside with respect to the core for heat treatment of themagnetic tape in a case of the heat treatment can be maintained and themagnetic tape can be wound around the cartridge reel of the magnetictape cartridge. Regarding the details of the core for temporary windingand the tension in a case of winding the magnetic tape around the core,the description described above regarding the core for heat treatmentcan be referred to. In an embodiment in which the heat treatment issubjected to the magnetic tape having a length of the “final productlength+α”, the length corresponding to “+α” may be cut in any stage. Forexample, In one embodiment, the magnetic tape having the final productlength may be wound around the cartridge reel of the magnetic tapecartridge from the core for temporary winding and the remaining lengthcorresponding the “+α” may be cut. From a viewpoint of decreasing theamount of the portion to be cut out and removed, the α is preferablyequal to or smaller than 20 m.

The specific embodiment of the heat treatment performed in a state ofbeing wound around the core member as described above is describedbelow.

An atmosphere temperature for performing the heat treatment(hereinafter, referred to as a “heat treatment temperature”) ispreferably equal to or higher than 40° C. and more preferably equal toor higher than 50° C. On the other hand, from a viewpoint of preventingthe excessive deformation, the heat treatment temperature is preferablyequal to or lower than 75° C. and more preferably equal to or lower than70° C.

A weight absolute humidity of the atmosphere for performing the heattreatment is preferably equal to or greater than 0.1 g/kg Dry air andmore preferably equal to or greater than 1 g/kg Dry air. The atmospherein which the weight absolute humidity is in the range described above ispreferable, because it can be prepared without using a special devicefor decreasing moisture. On the other hand, the weight absolute humidityis preferably equal to or smaller than 70 g/kg Dry air and morepreferably equal to or smaller than 66 g/kg Dry air, from a viewpoint ofpreventing a deterioration in workability by dew condensation. The heattreatment time is preferably equal to or longer than 0.3 hours and morepreferably equal to or longer than 0.5 hours. In addition, the heattreatment time is preferably equal to or shorter than 48 hours, from aviewpoint of production efficiency.

Regarding the control of the standard deviation of the curvaturedescribed above, as any value of the heat treatment temperature, heattreatment time, bending elastic modulus of a core for the heattreatment, and tension at the time of winding around the core for theheat treatment is large, the value of the curvature tends to furtherdecrease.

<Vertical Squareness Ratio>

In one embodiment, the vertical squareness ratio of the magnetic tapecan be, for example, 0.55 or more, and is preferably 0.60 or more. It ispreferable that the vertical squareness ratio of the magnetic tape is0.60 or more, from a viewpoint of improving the electromagneticconversion characteristics. In principle, an upper limit of thesquareness ratio is 1.00 or less. The vertical squareness ratio of themagnetic tape can be 1.00 or less, 0.95 or less, 0.90 or less, 0.85 orless, or 0.80 or less. It is preferable that the value of the verticalsquareness ratio of the magnetic tape is large from a viewpoint ofimproving the electromagnetic conversion characteristics. The verticalsquareness ratio of the magnetic tape can be controlled by a well-knownmethod such as performing a homeotropic alignment process.

In the invention and the specification, the “vertical squareness ratio”is squareness ratio measured in the vertical direction of the magnetictape. The “vertical direction” described with respect to the squarenessratio is a direction orthogonal to the surface of the magnetic layer,and can also be referred to as a thickness direction. In the inventionand the specification, the vertical squareness ratio is obtained by thefollowing method.

A sample piece having a size that can be introduced into an oscillationsample type magnetic-flux meter is cut out from the magnetic tape to bemeasured. Regarding the sample piece, using the oscillation sample typemagnetic-flux meter, a magnetic field is applied to a vertical directionof a sample piece (direction orthogonal to the surface of the magneticlayer) with a maximum applied magnetic field of 3979 kA/m, a measurementtemperature of 296 K, and a magnetic field sweep speed of 8.3 kA/m/sec,and a magnetization strength of the sample piece with respect to theapplied magnetic field is measured. The measured value of themagnetization strength is obtained as a value after diamagnetic fieldcorrection and a value obtained by subtracting magnetization of a sampleprobe of the oscillation sample type magnetic-flux meter as backgroundnoise. In a case where the magnetization strength at the maximum appliedmagnetic field is Ms and the magnetization strength at zero appliedmagnetic field is Mr, the squareness ratio SQ is a value calculated asSQ=Mr/Ms. The measurement temperature is referred to as a temperature ofthe sample piece, and by setting the ambient temperature around thesample piece to a measurement temperature, the temperature of the samplepiece can be set to the measurement temperature by realizing temperatureequilibrium.

Magnetic Tape Cartridge

According to another aspect of the invention, there is provided amagnetic tape cartridge comprising the magnetic tape described above.

The details of the magnetic tape included in the magnetic tape cartridgeare as described above.

In the magnetic tape cartridge, the magnetic tape is generallyaccommodated in a cartridge main body in a state of being wound around areel. The reel is rotatably provided in the cartridge main body. As themagnetic tape cartridge, a single reel type magnetic tape cartridgeincluding one reel in a cartridge main body and a twin reel typemagnetic tape cartridge including two reels in a cartridge main body arewidely used. In a case where the single reel type magnetic tapecartridge is mounted in the magnetic tape device in order to recordand/or reproduce data on the magnetic tape, the magnetic tape is drawnfrom the magnetic tape cartridge and wound around the reel on themagnetic tape device side. A magnetic head is disposed on a magnetictape transportation path from the magnetic tape cartridge to a windingreel. Feeding and winding of the magnetic tape are performed between areel (supply reel) on the magnetic tape cartridge side and a reel(winding reel) on the magnetic tape device side. In the meantime, forexample, the magnetic head comes into contact with and slides on thesurface of the magnetic layer of the magnetic tape, and accordingly, therecording and/or reproducing of data is performed. With respect to this,in the twin reel type magnetic tape cartridge, both reels of the supplyreel and the winding reel are provided in the magnetic tape cartridge.

In one embodiment, the magnetic tape cartridge can include a cartridgememory. The cartridge memory can be, for example, a non-volatile memory,and in one embodiment, head tilt angle adjustment information isrecorded in advance or head tilt angle adjustment information isrecorded. The head tilt angle adjustment information is information foradjusting the head tilt angle during the running of the magnetic tape inthe magnetic tape device. For example, as the head tilt angle adjustmentinformation, a value of the servo band spacing at each position in thelongitudinal direction of the magnetic tape at the time of datarecording can be recorded. For example, in a case where the datarecorded on the magnetic tape is reproduced, the value of the servo bandspacing is measured at the time of the reproducing, and the head tiltangle can be changed by the control device of the magnetic tape deviceso that an absolute value of a difference of the servo band spacing atthe time of recording at the same longitudinal position recorded in thecartridge memory is close to 0. The head tilt angle can be, for example,the angle θ described above.

The magnetic tape and the magnetic tape cartridge can be suitably usedin the magnetic tape device (that is, magnetic recording and reproducingsystem) for performing recording and/or reproducing data at differenthead tilt angles. In such a magnetic tape device, in one embodiment, itis possible to perform the recording and/or reproducing of data bychanging the head tilt angle during running of a magnetic tape. Forexample, the head tilt angle can be changed according to dimensionalinformation of the magnetic tape in the width direction obtained whilethe magnetic tape is running. In addition, for example, in a usageaspect, a head tilt angle during the recording and/or reproducing at acertain time and a head tilt angle during the recording and/orreproducing at the next time and subsequent times are changed, and thenthe head tilt angle may be fixed without changing during the running ofthe magnetic tape for the recording and/or reproducing of each time. Inany usage aspect, a magnetic tape having high running stability in acase of performing the recording and/or reproducing of data at differenthead tilt angles is preferable.

Magnetic Tape Device

According to still another aspect of the invention, there is provided amagnetic tape device comprising the magnetic tape. In the magnetic tapedevice, the recording of data on the magnetic tape and/or thereproducing of data recorded on the magnetic tape can be performed bybringing the surface of the magnetic layer of the magnetic tape intocontact with the magnetic head and sliding. For example, the magnetictape device can attachably and detachably include the magnetic tapecartridge according to one embodiment of the invention.

The magnetic tape cartridge can be attached to a magnetic tape deviceprovided with a magnetic head and used for performing the recordingand/or reproducing of data. In the invention and the specification, the“magnetic tape device” means a device capable of performing at least oneof the recording of data on the magnetic tape or the reproducing of datarecorded on the magnetic tape. Such a device is generally called adrive.

Magnetic Head

The magnetic tape device can include a magnetic head. The configurationof the magnetic head and the angle θ, which is the head tilt angle, areas described above with reference to FIGS. 1 to 3 . In a case where themagnetic head includes a reproducing element, as the reproducingelement, a magnetoresistive (MR) element capable of reading informationrecorded on the magnetic tape with excellent sensitivity is preferable.As the MR element, various well-known MR elements (for example, a GiantMagnetoresistive (GMR) element, or a Tunnel Magnetoresistive (TMR)element) can be used. Hereinafter, the magnetic head which records dataand/or reproduces the recorded data is also referred to as a “recordingand reproducing head”. The element for recording data (recordingelement) and the element for reproducing data (reproducing element) arecollectively referred to as a “magnetic head element”.

By reproducing data using the reproducing element having a narrowreproducing element width as the reproducing element, the data recordedat high density can be reproduced with high sensitivity. From thisviewpoint, the reproducing element width of the reproducing element ispreferably 0.8 μm or less. The reproducing element width of thereproducing element can be, for example, 0.3 μm or more. However, it isalso preferable to fall below this value from the above viewpoint.

Here, the “reproducing element width” refers to a physical dimension ofthe reproducing element width. Such physical dimensions can be measuredwith an optical microscope, a scanning electron microscope, or the like.

In a case of recording data and/or reproducing recorded data, first,tracking using a servo signal can be performed. That is, as the servosignal reading element follows a predetermined servo track, the magnetichead element can be controlled to pass on the target data track. Themovement of the data track is performed by changing the servo track tobe read by the servo signal reading element in the tape width direction.

In addition, the recording and reproducing head can perform therecording and/or reproducing with respect to other data bands. In thiscase, the servo signal reading element is moved to a predetermined servoband by using the UDIM information described above, and the trackingwith respect to the servo band may be started.

FIG. 5 shows an example of disposition of data bands and servo bands. InFIG. 5 , a plurality of servo bands 1 are disposed to be interposedbetween guide bands 3 in a magnetic layer of a magnetic tape MT. Aplurality of regions 2 each of which is interposed between two servobands are data bands. The servo pattern is a magnetized region and isformed by magnetizing a specific region of the magnetic layer by a servowrite head. The region magnetized by the servo write head (positionwhere a servo pattern is formed) is determined by standards. Forexample, in an LTO Ultrium format tape which is based on a localstandard, a plurality of servo patterns tilted in a tape width directionas shown in FIG. 6 are formed on a servo band, in a case ofmanufacturing a magnetic tape. Specifically, in FIG. 6 , a servo frameSF on the servo band 1 is configured with a servo sub-frame 1 (SSF1) anda servo sub-frame 2 (SSF2). The servo sub-frame 1 is configured with anA burst (in FIG. 6 , reference numeral A) and a B burst (in FIG. 6 ,reference numeral B). The A burst is configured with servo patterns A1to A5 and the B burst is configured with servo patterns B1 to B5.Meanwhile, the servo sub-frame 2 is configured with a C burst (in FIG. 6, reference numeral C) and a D burst (in FIG. 6 , reference numeral D).The C burst is configured with servo patterns C1 to C4 and the D burstis configured with servo patterns D1 to D4. Such 18 servo patterns aredisposed in the sub-frames in the arrangement of 5, 5, 4, 4, as the setsof 5 servo patterns and 4 servo patterns, and are used for recognizingthe servo frames. FIG. 6 shows one servo frame for explaining. However,in practice, in the magnetic layer of the magnetic tape in which thehead tracking in the timing-based servo system is performed, a pluralityof servo frames are disposed in each servo band in a running direction.In FIG. 6 , an arrow shows a magnetic tape running direction. Forexample, an LTO Ultrium format tape generally includes 5,000 or moreservo frames per a tape length of 1 m, in each servo band of themagnetic layer.

In the magnetic tape device, the head tilt angle can be changed whilethe magnetic tape is running in the magnetic tape device. The head tiltangle is, for example, an angle θ formed by the axis of the elementarray with respect to the width direction of the magnetic tape. Theangle θ is as described above. For example, by providing an angleadjustment unit for adjusting the angle of the module of the magnetichead in the recording and reproducing head unit of the magnetic head,the angle θ can be variably adjusted during the running of the magnetictape. Such an angle adjustment unit can include, for example, a rotationmechanism for rotating the module. For the angle adjustment unit, awell-known technology can be applied.

Regarding the head tilt angle during the running of the magnetic tape,in a case where the magnetic head includes a plurality of modules, theangle θ described with reference to FIGS. 1 to 3 can be specified forthe randomly selected module. The angle θ at the start of running of themagnetic tape, θ_(initial), can be set to 0° or more or more than 0°. Asthe θ_(initial) is large, a change amount of the effective distancebetween the servo signal reading elements with respect to a changeamount of the angle θ increases, and accordingly, it is preferable froma viewpoint of adjustment ability for adjusting the effective distancebetween the servo signal reading elements according to the dimensionchange of the width direction of the magnetic tape. From this viewpoint,the ° initial is preferably 1° or more, more preferably 5° or more, andeven more preferably 10° or more. Meanwhile, regarding an angle(generally referred to as a “lap angle”) formed by a surface of themagnetic layer and a contact surface of the magnetic head in a casewhere the magnetic tape runs and comes into contact with the magnetichead, a deviation in a tape width direction which is kept small iseffective in improving uniformity of friction in the tape widthdirection which is generated by the contact between the magnetic headand the magnetic tape during the running of the magnetic tape. Inaddition, it is desirable to improve the uniformity of the friction inthe tape width direction from a viewpoint of position followability andthe running stability of the magnetic head. From a viewpoint of reducingthe deviation of the lap angle in the tape width direction, θ_(initial)is preferably 45° or less, more preferably 40° or less, and even morepreferably 35° or less.

Regarding the change of the angle θ during the running of the magnetictape, while the magnetic tape is running in the magnetic tape device inorder to record data on the magnetic tape and/or to reproduce datarecorded on the magnetic tape, in a case where the angle θ of themagnetic head changes from θ_(initial) at the start of running, amaximum change amount Δθ of the angle θ during the running of themagnetic tape is a larger value among Δθ_(max) and Δθ_(min) calculatedby the following equation. A maximum value of the angle θ during therunning of the magnetic tape is θ_(max), and a minimum value thereof isθ_(min). In addition, “max” is an abbreviation for maximum, and “min” isan abbreviation for minimum.

Δθ_(max)=θ_(max)−θ_(initial)

Δθ_(min)=θ_(initial)−θ_(min)

In one embodiment, the Δθ can be more than 0.000°, and is preferably0.001° or more and more preferably 0.010° or more, from a viewpoint ofadjustment ability for adjusting the effective distance between theservo signal reading elements according to the dimension change in thewidth direction of the magnetic tape. In addition, from a viewpoint ofease of ensuring synchronization of recorded data and/or reproduced databetween a plurality of magnetic head elements during data recordingand/or reproducing, the Δθ is preferably 1.000° or less, more preferably0.900° or less, even more preferably 0.800° or less, still preferably0.700° or less, and still more preferably 0.600° or less.

In the examples shown in FIGS. 2 and 3 , the axis of the element arrayis tilted toward a magnetic tape running direction. However, the presentinvention is not limited to such an example. The present invention alsoincludes an embodiment in which the axis of the element array is tiltedin a direction opposite to the magnetic tape running direction in themagnetic tape device.

The head tilt angle θ_(initial) at the start of the running of themagnetic tape can be set by a control device or the like of the magnetictape device.

Regarding the head tilt angle during the running of the magnetic tape,FIG. 7 is an explanatory diagram of a method for measuring the angle θduring the running of the magnetic tape. The angle θ during the runningof the magnetic tape can be obtained, for example, by the followingmethod. In a case where the angle θ during traveling on the magnetictape is obtained by the following method, the angle θ is changed in arange of 0° to 90° during the running of the magnetic tape. That is, ina case where the axis of the element array is tilted toward the magnetictape running direction at the start of running of the magnetic tape, theelement array is not tilted so that the axis of the element array tiltstoward a direction opposite to the magnetic tape running direction atthe start of the running of the magnetic tape, during the running of themagnetic tape, and in a case where the axis of the element array istilted toward the direction opposite to the magnetic tape runningdirection at the start of running of the magnetic tape, the elementarray is not tilted so that the axis of the element array tilts towardthe magnetic tape running direction at the start of the running of themagnetic tape, during the running of the magnetic tape.

A phase difference (that is, time difference) ΔT of reproduction signalsof the pair of servo signal reading elements 1 and 2 is measured. Themeasurement of ΔT can be performed by a measurement unit provided in themagnetic tape device. A configuration of such a measurement unit is wellknown. A distance L between a central portion of the servo signalreading element 1 and a central portion of the servo signal readingelement 2 can be measured with an optical microscope or the like. In acase where a running speed of the magnetic tape is defined as a speed v,the distance in the magnetic tape running direction between the centralportions of the two servo signal reading elements is set to L sin θ, anda relationship of L sin θ=v×ΔT is satisfied. Therefore, the angle θduring the running of the magnetic tape can be calculated by a formula“θ=arcsin (vΔT/L)”. The right drawing of FIG. 7 shows an example inwhich the axis of the element array is tilted toward the magnetic taperunning direction. In this example, the phase difference (that is, timedifference) ΔT of a phase of the reproduction signal of the servo signalreading element 2 with respect to a phase of the reproduction signal ofthe servo signal reading element 1 is measured. In a case where the axisof the element array is tilted toward the direction opposite to therunning direction of the magnetic tape, θ can be obtained by the methoddescribed above, except for measuring ΔT as the phase difference (thatis, time difference) of the phase of the reproduction signal of theservo signal reading element 1 with respect to the phase of thereproduction signal of the servo signal reading element 2.

For a measurement pitch of the angle θ, that is, a measurement intervalof the angle θ in a tape longitudinal direction, a suitable pitch can beselected according to a frequency of tape width deformation in the tapelongitudinal direction. As an example, the measurement pitch can be, forexample, 250 μm.

Configuration of Magnetic Tape Device

A magnetic tape device 10 shown in FIG. 8 controls a recording andreproducing head unit 12 in accordance with a command from a controldevice 11 to record and reproduce data on a magnetic tape MT.

The magnetic tape device 10 has a configuration of detecting andadjusting a tension applied in a longitudinal direction of the magnetictape from spindle motors 17A and 17B and driving devices 18A and 18Bwhich rotatably control a magnetic tape cartridge reel and a windingreel.

The magnetic tape device 10 has a configuration in which the magnetictape cartridge 13 can be mounted.

The magnetic tape device 10 includes a cartridge memory read and writedevice 14 capable of performing reading and writing with respect to thecartridge memory 131 in the magnetic tape cartridge 13.

An end portion or a leader pin of the magnetic tape MT is pulled outfrom the magnetic tape cartridge 13 mounted on the magnetic tape device10 by an automatic loading mechanism or manually and passes on arecording and reproducing head through guide rollers 15A and 15B so thata surface of a magnetic layer of the magnetic tape MT comes into contactwith a surface of the recording and reproducing head of the recordingand reproducing head unit 12, and accordingly, the magnetic tape MT iswound around the winding reel 16.

The rotation and torque of the spindle motor 17A and the spindle motor17B are controlled by a signal from the control device 11, and themagnetic tape MT runs at random speed and tension. A servo patternpreviously formed on the magnetic tape can be used to control the tapespeed and control the head tilt angle. A tension detection mechanism maybe provided between the magnetic tape cartridge 13 and the winding reel16 to detect the tension. The tension may be controlled by using theguide rollers 15A and 15B in addition to the control by the spindlemotors 17A and 17B.

The cartridge memory read and write device 14 is configured to be ableto read and write information of the cartridge memory 131 according tocommands from the control device 11. As a communication system betweenthe cartridge memory read and write device 14 and the cartridge memory131, for example, an international organization for standardization(ISO) 14443 system can be used.

The control device 11 includes, for example, a controller, a storageunit, a communication unit, and the like.

The recording and reproducing head unit 12 is composed of, for example,a recording and reproducing head, a servo tracking actuator foradjusting a position of the recording and reproducing head in a trackwidth direction, a recording and reproducing amplifier 19, a connectorcable for connecting to the control device 11. The recording andreproducing head is composed of, for example, a recording element forrecording data on a magnetic tape, a reproducing element for reproducingdata of the magnetic tape, and a servo signal reading element forreading a servo signal recorded on the magnetic tape. For example, oneor more of each of the recording elements, the reproducing element, andthe servo signal reading element are mounted in one magnetic head.Alternatively, each element may be separately provided in a plurality ofmagnetic heads according to a running direction of the magnetic tape.

The recording and reproducing head unit 12 is configured to be able torecord data on the magnetic tape MT according to a command from thecontrol device 11. In addition, the data recorded on the magnetic tapeMT can be reproduced according to a command from the control device 11.

The control device 11 has a mechanism of controlling the servo trackingactuator so as to obtain a running position of the magnetic tape from aservo signal read from a servo band during the running of the magnetictape MT and position the recording element and/or the reproducingelement at a target running position (track position). The control ofthe track position is performed by feedback control, for example. Thecontrol device 11 has a mechanism of obtaining a servo band spacing fromservo signals read from two adjacent servo bands during the running ofthe magnetic tape MT. The control device 11 can store the obtainedinformation of the servo band spacing in the storage unit inside thecontrol device 11, the cartridge memory 131, an external connectiondevice, and the like. In addition, the control device 11 can change thehead tilt angle according to the dimensional information in the widthdirection of the magnetic tape during the running. Accordingly, it ispossible to bring the effective distance between the servo signalreading elements closer to or match the spacing of the servo bands. Thedimensional information can be obtained by using the servo patternpreviously formed on the magnetic tape. For example, by doing so, theangle θ formed by the axis of the element array with respect to thewidth direction of the magnetic tape can be changed during the runningof the magnetic tape in the magnetic tape device according todimensional information of the magnetic tape in the width directionobtained during the running. The head tilt angle can be adjusted, forexample, by feedback control. Alternatively, for example, the head tiltangle can also be adjusted by a method disclosed in JP2016-524774A orUS2019/0164573A1.

EXAMPLES

Hereinafter, the invention will be described with reference to examples.However, the invention is not limited to the embodiments shown in theexamples. “Parts” and “%” described below indicate “parts by mass” and“% by mass”. In addition, steps and evaluations described below areperformed in an environment of an atmosphere temperature of 23° C.±1°C., unless otherwise noted. “eq” described below indicates equivalentand a unit not convertible into SI unit.

Ferromagnetic Powder

In Table 1, “BaFe” is a hexagonal barium ferrite powder (coercivity Hc:196 kA/m, an average particle size (average plate diameter): 24 nm).

In Table 1, “SrFe1” is a hexagonal strontium ferrite powder produced bythe following method.

1,707 g of SrCO₃, 687 g of H₃BO₃, 1,120 g of Fe₂O₃, 45 g of Al(OH)₃, 24g of BaCO₃, 13 g of CaCO₃, and 235 g of Nd₂O₃ were weighed and mixed ina mixer to obtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucibleat a melting temperature of 1,390° C., and a tap hole provided on thebottom of the platinum crucible was heated while stirring the melt, andthe melt was tapped in a rod shape at approximately 6 g/sec. The tapliquid was rolled and cooled with a water cooling twin roller to preparean amorphous body.

280 g of the prepared amorphous body was put into an electronic furnace,heated to 635° C. (crystallization temperature) at a rate of temperaturerise of 3.5° C./min, and held at the same temperature for 5 hours, andhexagonal strontium ferrite particles were precipitated (crystallized).

Then, the crystallized material obtained as described above includingthe hexagonal strontium ferrite particles was coarse-pulverized with amortar, 1000 g of zirconia beads having a particle diameter of 1 mm and800 ml of an acetic acid aqueous solution having a concentration of 1%were added to a glass bottle, and a dispersion process was performed ina paint shaker for 3 hours. After that, the obtained dispersion liquidand the beads were separated and put in a stainless still beaker. Thedispersion liquid was left at a liquid temperature of 100° C. for 3hours, subjected to a dissolving process of a glass component,precipitated with a centrifugal separator, decantation was repeated forcleaning, and drying was performed in a heating furnace at a furnaceinner temperature of 110° C. for 6 hours, to obtain hexagonal strontiumferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as describedabove, an average particle size was 18 nm, an activation volume was 902nm³, an anisotropy constant Ku was 2.2×10⁵ J/m³, and a massmagnetization σs was 49 A·m²/kg.

12 mg of a sample powder was collected from the hexagonal strontiumferrite powder obtained as described above, the element analysis of afiltrate obtained by the partial dissolving of this sample powder underthe dissolving conditions described above was performed by the ICPanalysis device, and a surface layer portion content of a neodymium atomwas obtained.

Separately, 12 mg of a sample powder was collected from the hexagonalstrontium ferrite powder obtained as described above, the elementanalysis of a filtrate obtained by the total dissolving of this samplepowder under the dissolving conditions described above was performed bythe ICP analysis device, and a bulk content of a neodymium atom wasobtained.

The content (bulk content) of the neodymium atom in the hexagonalstrontium ferrite powder obtained as described above with respect to 100atom % of iron atom was 2.9 atom %. In addition, the surface layerportion content of the neodymium atom was 8.0 atom %. A ratio of thesurface layer portion content and the bulk content, “surface layerportion content/bulk content” was 2.8 and it was confirmed that theneodymium atom is unevenly distributed on the surface layer of theparticles.

A crystal structure of the hexagonal ferrite shown by the powderobtained as described above was confirmed by scanning CuKα ray under theconditions of a voltage of 45 kV and intensity of 40 mA and measuring anX-ray diffraction pattern under the following conditions (X-raydiffraction analysis). The powder obtained as described above showed acrystal structure of magnetoplumbite type (M type) hexagonal ferrite. Inaddition, a crystal phase detected by the X-ray diffraction analysis wasa magnetoplumbite type single phase.

PANalytical X'Pert Pro diffractometer, PIXcel detector

Soller slit of incident beam and diffraction beam: 0.017 radians

Fixed angle of dispersion slit: ¼ degrees

Mask: 10 mm

Scattering prevention slit: ¼ degrees

Measurement mode: continuous

Measurement time per 1 stage: 3 seconds

Measurement speed: 0.017 degrees per second

Measurement step: 0.05 degree

In Table 1, “SrFe2” is a hexagonal strontium ferrite powder produced bythe following method.

1,725 g of SrCO₃, 666 g of H₃BO₃, 1,332 g of Fe₂O₃, 52 g of Al(OH)₃, 34g of CaCO₃, and 141 g of BaCO₃ were weighed and mixed in a mixer toobtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucibleat a melting temperature of 1,380° C., and a tap hole provided on thebottom of the platinum crucible was heated while stirring the melt, andthe melt was tapped in a rod shape at approximately 6 g/sec. The tapliquid was rolled and cooled with a water cooling twin roller to preparean amorphous body.

280 g of the obtained amorphous body was put into an electronic furnace,heated to 645° C. (crystallization temperature), and held at the sametemperature for 5 hours, and hexagonal strontium ferrite particles wereprecipitated (crystallized).

Then, the crystallized material obtained as described above includingthe hexagonal strontium ferrite particles was coarse-pulverized with amortar, 1000 g of zirconia beads having a particle diameter of 1 mm and800 ml of an acetic acid aqueous solution having a concentration of 1%were added to a glass bottle, and a dispersion process was performed ina paint shaker for 3 hours. After that, the obtained dispersion liquidand the beads were separated and put in a stainless still beaker. Thedispersion liquid was left at a liquid temperature of 100° C. for 3hours, subjected to a dissolving process of a glass component,precipitated with a centrifugal separator, decantation was repeated forcleaning, and drying was performed in a heating furnace at a furnaceinner temperature of 110° C. for 6 hours, to obtain hexagonal strontiumferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as describedabove, an average particle size was 19 nm, an activation volume was1,102 nm³, an anisotropy constant Ku was 2.0×10⁵ J/m³, and a massmagnetization σs was 50 A×m²/kg.

In Table 1, “ε-iron oxide” is an ε-iron oxide powder produced by thefollowing method.

4.0 g of ammonia aqueous solution having a concentration of 25% wasadded to a material obtained by dissolving 8.3 g of iron (III) nitratenonahydrate, 1.3 g of gallium (III) nitrate octahydrate, 190 mg ofcobalt (II) nitrate hexahydrate, 150 mg of titanium (IV) sulfate, and1.5 g of polyvinyl pyrrolidone (PVP) in 90 g of pure water, whilestirring by using a magnetic stirrer, in an atmosphere under theconditions of an atmosphere temperature of 25° C., and the mixture wasstirred for 2 hours still under the temperature condition of theatmosphere temperature of 25° C. A citric acid aqueous solution obtainedby dissolving 1 g of citric acid in 9 g of pure water was added to theobtained solution and stirred for 1 hour. The powder precipitated afterthe stirring was collected by centrifugal separation, washed with purewater, and dried in a heating furnace at a furnace inner temperature of80° C.

800 g of pure water was added to the dried powder and the powder wasdispersed in water again, to obtain a dispersion liquid. The obtaineddispersion liquid was heated to a liquid temperature of 50° C., and 40 gof ammonia aqueous solution having a concentration of 25% was addeddropwise while stirring. The stirring was performed for 1 hour whileholding the temperature of 50° C., and 14 mL of tetraethoxysilane (TEOS)was added dropwise and stirred for 24 hours. 50 g of ammonium sulfatewas added to the obtained reaction solution, the precipitated powder wascollected by centrifugal separation, washed with pure water, and driedin a heating furnace at a furnace inner temperature of 80° C. for 24hours, and a precursor of ferromagnetic powder was obtained.

The heating furnace at a furnace inner temperature of 1,000° C. wasfilled with the obtained precursor of ferromagnetic powder in theatmosphere and subjected to heat treatment for 4 hours.

The heat-treated precursor of ferromagnetic powder was put into sodiumhydroxide (NaOH) aqueous solution having a concentration of 4 mol/L, theliquid temperature was held at 70° C., stirring was performed for 24hours, and accordingly, a silicon acid compound which was an impuritywas removed from the heat-treated precursor of ferromagnetic powder.

After that, by the centrifugal separation process, ferromagnetic powderobtained by removing the silicon acid compound was collected and washedwith pure water, and ferromagnetic powder was obtained.

The composition of the obtained ferromagnetic powder was confirmed byInductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), andGa, Co, and Ti substitution type ε-iron oxide(ε-Ga_(0.28)Co_(0.05)Ti_(0.05)Fe_(1.62)O₃) was obtained. In addition,the X-ray diffraction analysis was performed under the same conditionsas disclosed regarding SrFe1 above, and it was confirmed that theobtained ferromagnetic powder has a crystal structure of a single phasewhich is an E phase not including a crystal structure of an α phase anda γ phase (ε-iron oxide type crystal structure) from the peak of theX-ray diffraction pattern.

Regarding the obtained (ε-iron oxide powder, an average particle sizewas 12 nm, an activation volume was 746 nm³, an anisotropy constant Kuwas 1.2×10⁵ J/m³, and a mass magnetization σs was 16 A×m²/kg.

The activation volume and the anisotropy constant Ku of the hexagonalstrontium ferrite powder and the ε-iron oxide powder are values obtainedby the method described above regarding each ferromagnetic powder byusing an oscillation sample type magnetic-flux meter (manufactured byToei Industry Co., Ltd.).

The mass magnetization σs is a value measured using a vibrating samplemagnetometer (manufactured by Toei Industry Co., Ltd.) at a magneticfield strength of 15 kOe.

Example 1

Preparation of Alumina Dispersion

3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo ChemicalIndustry Co., Ltd.), 31.3 parts of a 32% solution (solvent is a mixedsolvent of methyl ethyl ketone and toluene) of a polyester polyurethaneresin including a SO₃Na group as a polar group (UR-4800 manufactured byToyobo Co., Ltd. (polar group amount: 80 meq/kg)), and 570.0 parts of amixed solution of methyl ethyl ketone and cyclohexanone (mass ratio of1:1) as a solvent were mixed with 100.0 parts of alumina powder (HIT-80manufactured by Sumitomo Chemical Co., Ltd.) having a gelatinizationratio of 65% and a Brunauer-Emmett-Teller (BET) specific surface area of20 m²/g, and dispersed in the presence of zirconia beads by a paintshaker for 5 hours. After the dispersion, the dispersion liquid and thebeads were separated by a mesh and an alumina dispersion was obtained.

Magnetic Layer Forming Composition

Magnetic Liquid

Ferromagnetic powder (see Table 1): 100.0 parts

SO₃Na group-containing polyurethane resin: 14.0 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g

Cyclohexanone: 150.0 parts

Methyl ethyl ketone: 150.0 parts

Abrasive solution

Alumina dispersion prepared above: 6.0 parts

Silica Sol (Projection Formation Agent Liquid)

Colloidal silica (average particle size: 120 nm): 2.0 parts

Methyl ethyl ketone: 1.4 parts

Other Components

Stearic acid: 2.0 parts

Stearic acid amide: 0.2 parts

Butyl stearate: 2.0 parts

Polyisocyanate (CORONATE (registered product) L manufactured by TosohCorporation): 2.5 parts

Finishing Additive Solvent

Cyclohexanone: 200.0 parts

Methyl ethyl ketone: 200.0 parts

Non-Magnetic Layer Forming Composition

α-Iron oxide powder (average particle volume: see Table 1): 80.0 parts

Carbon black (average particle size: 20 nm, pH: see Table 1): 20.0 parts

Electron ray curable vinyl chloride copolymer: 13.0 parts

Electron beam curable polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Cyclohexanone: 140.0 parts

Methyl ethyl ketone: 170.0 parts

Butyl stearate: 2.0 parts Stearic acid: 1.0 part

Back Coating Layer Forming Composition

Non-magnetic inorganic powder (α-iron oxide powder): 80.0 parts

(Average particle size: 0.15 μm, average acicular ratio: 7, BET specificsurface area:

52 m²/g)

Carbon black (average particle size: 20 nm): 20.0 parts

Carbon black (average particle size: 100 nm): 3.0 parts

A vinyl chloride copolymer: 13.0 parts

A sulfonic acid group-containing polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Cyclohexanone: 140.0 parts

Methyl ethyl ketone: 170.0 parts

Stearic acid: 3.0 parts

Polyisocyanate (CORONATE (registered product) L manufactured by TosohCorporation): 5.0 parts

Methyl ethyl ketone: 400.0 parts

Preparation of Each Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod.

The magnetic liquid was prepared by dispersing (beads-dispersing) thecomponent by using a batch type vertical sand mill for 24 hours. Asdispersion beads, zirconia beads having a bead diameter of 0.5 mm wereused. The prepared magnetic liquid, the abrasive solution, and othercomponents (silica sol, other components, and finishing additivesolvent) were mixed with each other and beads-dispersed for 5 minutes byusing the sand mill, and the treatment (ultrasonic dispersion) wasperformed with a batch type ultrasonic device (20 kHz, 300 W) for 0.5minutes. After that, the obtained mixed solution was filtered by using afilter having a hole diameter of 0.5 μm, and the magnetic layer formingcomposition was prepared.

The non-magnetic layer forming composition was prepared by the followingmethod.

The components excluding the lubricant (butyl stearate and stearic acid)were kneaded and diluted with an open kneader, and then dispersed with atransverse beads mill disperser. Then, the lubricant (butyl stearate andstearic acid) was added, and the mixture was stirred and mixed with adissolver stirrer to prepare a non-magnetic layer forming composition.

The back coating layer forming composition was prepared by the followingmethod.

The components excluding the lubricant (stearic acid), polyisocyanate,and methyl ethyl ketone (400.0 parts) were kneaded and diluted with anopen kneader, and then dispersed with a transverse beads mill disperser.Then, the lubricant (stearic acid), polyisocyanate, and methyl ethylketone (400.0 parts) were added, and the mixture was stirred and mixedwith a dissolver stirrer to prepare a back coating layer formingcomposition.

Manufacturing of Magnetic Tape and Magnetic Tape Cartridge

The non-magnetic layer forming composition was applied to a biaxialstretching support made of polyethylene naphthalate having a thicknessof 4.1 μm so that the thickness after the drying is 0.7 μm and was driedto emit an electron ray to have energy of 40 kGy at an accelerationvoltage of 125 kV. The magnetic layer forming composition was appliedonto that so that the thickness after the drying is 0.1 μm and dried,and the back coating layer forming composition was applied to a surfaceof the support opposite to the surface where the non-magnetic layer andthe magnetic layer are formed, so that the thickness after the drying is0.3 μm and dried.

Then, a calender process was performed by using a 7-stage calender rollconfigured of only a metal roll, at a calendar speed of 80 m/min, linearpressure of 294 kN/m, and a calender temperature (surface temperature ofa calender roll) of 80° C. Then, the heat treatment was performed in theenvironment of the ambient temperature of 70° C. for 36 hours. After theheat treatment, slitting is performed to have a width of ½ inches.

The surface of the magnetic layer of the magnetic tape having a width of½ inches thus obtained was subjected to the burnishing process and thewiping process. The burnishing process and the wiping process wereperformed in a process device having a configuration shown in FIG. 1 ofJP-H06-52544A, by using a commercially available abrasive tape (productname MA22000 manufactured by Fujifilm Holdings Corporation, abrasive:diamond/Cr₂O₃/α-iron oxide) as an abrasive tape, by using a commerciallyavailable sapphire blade (manufactured by Kyocera Corporation, width of5 mm, length of 35 mm, an angle of a distal end of 60 degrees) as ablade for grinding, and by using a commercially available wipingmaterial (product name WRP736 manufactured by Kuraray Co., Ltd.) as awiping material. For the process conditions, the process conditions inExample 12 of JP-H06-52544A was used, except that the burnishing processtensions during the burnishing process on the central region and theregion in the vicinity of the edge of the surface of the magnetic layerwere set to values described in Table 1.

After that, by recording a servo signal on a magnetic layer of theobtained magnetic tape with a commercially available servo writer, andincluding a servo pattern (timing-based servo pattern) having thedisposition and shape according to the linear tape-open (LTO) Ultriumformat on the servo band was obtained.

Accordingly, a magnetic tape including data bands, servo bands, andguide bands in the disposition according to the LTO Ultrium format inthe magnetic layer, and including servo patterns (timing-based servopattern) having the disposition and the shape according to the LTOUltrium format on the servo band was obtained. The servo pattern formedby doing so is a servo pattern disclosed in Japanese IndustrialStandards (JIS) X6175:2006 and Standard ECMA-319 (June 2001).

The total number of servo bands is five, and the total number of databands is four.

A magnetic tape (length of 960 m) on which the servo signal was recordedas described above was wound around the reel of the magnetic tapecartridge (LTO Ultrium 8 data cartridge), and a leader tape according toArticle 9 of Section 3 of standard European Computer ManufacturersAssociation (ECMA)-319 (June 2001) was bonded to an end thereof by usinga commercially available splicing tape.

By doing so, a magnetic tape cartridge in which the magnetic tape waswound around the reel was manufactured.

Examples 2 to 24 and Comparative Examples 1 to 10

A magnetic tape and a magnetic tape cartridge were obtained by themethod described in Example 1, except that the items shown in Table 1were changed as shown in Table 1.

For Examples 18 to 24, the step after recording the servo signal waschanged as follows. That is, the heat treatment was performed afterrecording the servo signal. On the other hand, in Examples 1 to 17 andComparative Examples 1 to 10, since such heat treatment was notperformed, “None” was shown in the column of “heat treatment condition”in Table 1.

For Examples 18 to 24, the magnetic tape (length of 970 m) afterrecording the servo signal as described in Example 1 was wound around acore for the heat treatment and heat-treated in a state of being woundaround the core. As the core for heat treatment, a solid core member(outer diameter: 50 mm) formed of a resin and having a value of abending elastic modulus shown in Table 1 was used, and the tension in acase of the winding was set as a value shown in Table 1. The heattreatment temperature and heat treatment time in the heat treatment wereset to values shown in Table 1. The weight absolute humidity in theatmosphere in which the heat treatment was performed was 10 g/kg Dryair.

After the heat treatment, the magnetic tape and the heat treatment corewere sufficiently cooled, and then the magnetic tape was detached fromthe heat treatment core and wound around a core for temporary winding.As the core for temporary winding, a solid core member having the sameouter diameter and formed of the same material as the core for heattreatment was used, and the tension at the time of winding was set as0.6 N.

After that, the magnetic tape having the final product length (960 m)was wound around the reel of the magnetic tape cartridge (LTO Ultrium 8data cartridge) from the core for temporary winding, the remaininglength of 10 m was cut out, and a leader tape according to Article 9 ofSection 3 of standard European Computer Manufacturers Association(ECMA)-319 (June 2001) was bonded to an end of a cut side thereof byusing a commercially available splicing tape.

By doing so, a magnetic tape cartridge in which the magnetic tape waswound around the reel was manufactured.

For each of the Examples and Comparative Examples, four magnetic tapecartridges were manufactured, one was used for the evaluation of runningstability below, and the other three were used for the evaluations (1)to (3) of the magnetic tape.

Evaluation of Running Stability

In an environment with a temperature of 40° C. and a relative humidityof 10%, the running stability was evaluated by the following method.

The temperature and the humidity described above are examples of thetemperature and the humidity in the high temperature and low humidityenvironment. In addition, the following head tilt angle is used as anexemplary value of an angle that can be used in a case of performing therecording and/or reproducing of data at different head tilt angles.Therefore, the temperature and the humidity of the environment and thehead tilt angle in a case of performing the recording of the data on themagnetic tape and the reproducing of the recorded data according to oneaspect of the present invention are not limited to the above values andthe following values.

Using each of the magnetic tape cartridges of the examples and thecomparative examples, data recording and reproducing were performedusing the magnetic tape device having the configuration shown in FIG. 8. The arrangement order of the modules included in the recording andreproducing head mounted on the recording and reproducing head unit is“recording module-reproducing module-recording module” (total number ofmodules: 3). The number of magnetic head elements in each module is 32(Ch0 to Ch31), and the element array is configured by sandwiching thesemagnetic head elements between the pair of servo signal readingelements. The reproducing element width of the reproducing elementincluded in the reproducing module is 0.8 μm.

By the following method, the performing of the recording and reproducingof data and evaluating of the running stability during the reproducingwere performed four times in total by sequentially changing the headtilt angle in the order of 0°, 15°, 30°, and 45°. The head tilt angle isan angle θ formed by the axis of the element array of the reproducingmodule with respect to the width direction of the magnetic tape at thestart of each time of running. The angle θ was set by the control deviceof the magnetic tape device at the start of each time of running of themagnetic tape, and the head tilt angle was fixed during each time ofrunning of the magnetic tape.

The magnetic tape cartridge was set in the magnetic tape device and themagnetic tape was loaded. Next, while performing servo tracking, therecording and reproducing head unit records pseudo random data having aspecific data pattern on the magnetic tape. The tension applied in thetape longitudinal direction at that time is a constant value. At thesame time with the recording of the data, the value of the servo bandspacing of the entire tape length was measured every 1 m of thelongitudinal position and recorded in the cartridge memory.

Next, while performing servo tracking, the recording and reproducinghead unit reproduces the data recorded on the magnetic tape. The tensionapplied in the tape longitudinal direction at that time is a constantvalue.

The running stability was evaluated using a standard deviation of areading position PES (Position Error Signal) in the width directionbased on the servo signal obtained by the servo signal reading elementduring the reproducing (hereinafter, referred to as “σPES”) as anindicator.

PES is obtained by the following method.

In order to obtain the PES, the dimensions of the servo pattern arerequired. The standard of the dimension of the servo pattern variesdepending on generation of LTO. Therefore, first, an average distance ACbetween the corresponding four stripes of the A burst and the C burstand an azimuth angle α of the servo pattern are measured using amagnetic force microscope or the like.

An average time between 5 stripes corresponding to the A burst and the Bburst over the length of 1 LPOS word is defined as a. An average timebetween 4 stripes corresponding to the A burst and the C burst over thelength of 1 LPOS word is defined as b. At this time, the value definedby AC×(½−a/b)/(2×tan(α)) represents a reading position PES (PositionError Signal) in the width direction based on the servo signal obtainedby the servo signal reading element over the length of 1 LPOS word.Regarding the magnetic tape, an end on a side wound around a reel of themagnetic tape cartridge is referred to as an inner end, an end on theopposite side thereof is referred to as an outer end, the outer end isset to 0 m, and in a region in a tape longitudinal direction over alength of 30 m to 200 m, the standard deviation of PES (σPES) obtainedby the method described above was calculated.

The arithmetic average of σPES obtained during four times of recordingand reproducing in total is shown in the column of “σPES” in Table 1. Ina case where the σPES is less than 70 nm, it can be determined that therunning stability is excellent.

Evaluation of Magnetic Tape

(1) Edge Portion Ra, Central Portion Ra, Ra Ratio (Central PortionRa/Edge Portion Ra)

The magnetic tape was extracted from each of the magnetic tapecartridges of Examples and Comparative Examples, the edge portion Ra andthe central portion Ra were obtained by the method described above, andthe Ra ratio (central portion Ra/edge portion Ra) was calculated fromthe obtained values.

(2) Standard Deviation of Curvature of Magnetic Tape in LongitudinalDirection

The magnetic tape was taken out from the magnetic tape cartridge, andthe standard deviation of the curvature of the magnetic tape in thelongitudinal direction was determined by the method described above.

(3) Tape Thickness

10 tape samples (length: 5 cm) were cut out from any part of themagnetic tape extracted from each of the magnetic tape cartridges ofExamples and Comparative Examples, and these tape samples were stackedto measure the thickness. The thickness was measured using a digitalthickness gauge of a Millimar 1240 compact amplifier manufactured byMARH and a Millimar 1301 induction probe. The value (thickness per tapesample) obtained by calculating 1/10 of the measured thickness wasdefined as the tape thickness. For all of the magnetic tape, the tapethickness was 5.2 μm.

The result described above is shown in Table 1 (Tables 1-1 and 1-2).

TABLE 1-1 Magnetic layer forming composition Ra Heat treatmentconditions Stan- Burnishing ratio Non-magnetic layer Ten- dard processCentral α-iron bend- sion devi- tension [gf] Ra (nm) portion oxide ingduring ation Region Cen- Edge Ra/ powder Car- elastic wind- of cur-Ferro- Cen- in tral por- edge Average bon mod- ing vature magnetic tralvicinity portion tion portion particle black Temper- ulus around (mm/σPES powder region of edge Ra Ra Ra volume pH ature Time of core core m)(nm) Example 1 BaFe 122 100 1.12 1.50 0.75 2.0 × 10⁻⁶ μm³ 5.0 None NoneNone None 6 54 Example 2 BaFe 111 100 1.30 1.50 0.87 2.0 × 10⁻⁶ μm³ 5.0None None None None 6 53 Example 3 BaFe 111 107 1.30 1.37 0.95 2.0 ×10⁻⁶ μm³ 5.0 None None None None 6 54 Example 4 BaFe 124 111 1.10 1.300.85 2.0 × 10⁻⁶ μm³ 5.0 None None None None 6 53 Example 5 BaFe 131 1171.00 1.20 0.83 2.0 × 10⁻⁶ μm³ 5.0 None None None None 6 53 Example 6BaFe 156 131 0.75 1.00 0.75 2.0 × 10⁻⁶ μm³ 5.0 None None None None 6 52Example 7 BaFe 156 140 0.75 0.90 0.83 2.0 × 10⁻⁶ μm³ 5.0 None None NoneNone 6 53 Example 8 BaFe 156 151 0.75 0.79 0.95 2.0 × 10⁻⁶ μm³ 5.0 NoneNone None None 6 52 Example 9 BaFe 233 210 0.30 0.40 0.75 2.0 × 10⁻⁶ μm³5.0 None None None None 6 53 Example 10 BaFe 233 228 0.30 0.32 0.94 2.0× 10⁻⁶ μm³ 5.0 None None None None 6 52 Example 11 BaFe 150 131 0.700.90 0.78 1.0 × 10⁻⁶ μm³ 5.0 None None None None 6 46 Example 12 BaFe156 140 0.65 0.80 0.81 1.0 × 10⁻⁶ μm³ 5.0 None None None None 6 44Example 13 BaFe 156 151 0.65 0.69 0.94 1.0 × 10⁻⁶ μm³ 5.0 None None NoneNone 6 45 Example 14 BaFe 156 140 0.65 0.80 0.81 1.0 × 10⁻⁶ μm³ 5.0 NoneNone None None 6 42 Example 15 BaFe 156 151 0.65 0.69 0.94 1.0 × 10⁻⁶μm³ 5.0 None None None None 6 43 Example 16 BaFe 156 140 0.60 0.75 0.801.0 × 10⁻⁶ μm³ 3.5 None None None None 6 35 Example 17 BaFe 145 141 0.700.74 0.95 1.0 × 10⁻⁶ μm³ 3.5 None None None None 6 34 Example 18 BaFe156 140 0.60 0.75 0.80 1.0 × 10⁻⁶ μm³ 3.5 50° C. 5 0.8 0.6N 5 33 hoursGPa Example 19 BaFe 156 140 0.60 0.75 0.80 1.0 × 10⁻⁶ μm³ 3.5 60° C. 50.8 0.6N 4 33 hours GPa Example 20 BaFe 156 140 0.60 0.75 0.80 1.0 ×10⁻⁶ μm³ 3.5 70° C. 5 0.8 0.6N 3 32 hours GPa Example 21 BaFe 156 1400.60 0.75 0.80 1.0 × 10⁻⁶ μm³ 3.5 70° C. 15 0.8 0.8N 2 30 hours GPaExample 22 SrFe1 111 100 1.15 1.35 0.85 1.0 × 10⁻⁶ μm³ 3.5 70° C. 15 0.80.8N 2 30 hours GPa Example 23 SrFe2 111 100 1.15 1.35 0.80 1.0 × 10⁻⁶μm³ 3.5 70° C. 15 0.8 0.8N 2 30 hours GPa Example 24 ε-iron 111 100 1.151.35 0.85 1.0 × 10⁻⁶ μm³ 3.5 70° C. 15 0.8 0.8N 2 30 oxide hours GPapowder

TABLE 1-2 Magnetic layer forming composition Ra Heat treatmentconditions Stan- Burnishing ratio Non-magnetic layer Ten- dard processCentral α-iron bend- sion devi- tension [gf] Ra (nm) portion oxide ingduring ation Region Cen- Edge Ra/ powder Car- elastic wind- of cur-Ferro- Cen- in tral por- edge Average bon mod- ing vature magnetic tralvicinity portion tion portion particle black Temper- ulus around (mm/σPES powder region of edge Ra Ra Ra volume pH ature Time of core core m)(nm) Comparative BaFe 100 100 1.60 1.60 1.00 5.0 × 10⁻⁶ μm³ 7.5 NoneNone None None 6 80 Example 1 Comparative BaFe 105 105 1.50 1.50 1.005.0 × 10⁻⁶ μm³ 7.5 None None None None 6 86 Example 2 Comparative BaFe117 117 1.30 1.30 1.00 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 90Example 3 Comparative BaFe 100 117 1.60 1.30 1.23 5.0 × 10⁻⁶ μm³ 7.5None None None None 6 87 Example 4 Comparative BaFe 111 117 1.40 1.301.08 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 88 Example 5 ComparativeBaFe 117 100 1.30 1.60 0.81 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 83Example 6 Comparative BaFe 140 162 1.00 0.80 1.25 5.0 × 10⁻⁶ μm³ 7.5None None None None 6 85 Example 7 Comparative BaFe 175 175 0.70 0.701.00 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 86 Example 8 ComparativeBaFe 175 140 0.70 1.00 0.70 5.0 × 10⁻⁶ μm³ 7.5 None None None None 6 90Example 9 Comparative BaFe 300 280 0.20 0.25 0.80 5.0 × 10⁻⁶ μm³ 7.5None None None None 6 93 Example 10

From the results shown in Table 1, it can be confirmed that the magnetictape of the examples showed excellent running stability in a case wherethe magnetic tape was caused to run at different head tilt angles in thehigh temperature and low humidity environment.

The magnetic tape cartridge was manufactured by the method described inExample 1, except that, during the manufacturing of the magnetic tape,after forming the coating layer by applying the magnetic layer formingcomposition, a homeotropic alignment process was performed by applying amagnetic field having a magnetic field strength of 0.3 T in a verticaldirection with respect to a surface of a coating layer, while thecoating layer of the magnetic layer forming composition is wet, andthen, the drying was performed to form the magnetic layer.

A sample piece was cut out from the magnetic tape taken out from themagnetic tape cartridge. For this sample piece, a vertical squarenessratio was obtained by the method described above using aTM-TRVSM5050-SMSL type manufactured by Tamagawa Seisakusho Co., Ltd. asan oscillation sample type magnetic-flux meter and it was 0.60.

The magnetic tape was also taken out from the magnetic tape cartridge ofExample 1, and the vertical squareness ratio was obtained in the samemanner for the sample piece cut out from the magnetic tape, and it was0.55.

The magnetic tapes taken out from the above two magnetic tape cartridgeswere attached to each of the ½-inch reel testers, and theelectromagnetic conversion characteristics (signal-to-noise ratio (SNR))were evaluated by the following methods. As a result, regarding themagnetic tape manufactured by performing the homeotropic alignmentprocess, a value of SNR 2 dB higher than that of the magnetic tapemanufactured without the homeotropic alignment process was obtained.

In an environment of a temperature of 23° C. and a relative humidity of50%, a tension of 0.7 N was applied in the longitudinal direction of themagnetic tape, and recording and reproduction were performed for 10passes. A relative speed of the magnetic head and the magnetic tape wasset as 6 m/sec. The recording was performed by using a metal-in-gap(MIG) head (gap length of 0.15 μm, track width of 1.0 μm) as therecording head and by setting a recording current as an optimalrecording current of each magnetic tape. The reproduction was performedusing a giant-magnetoresistive (GMR) head (element thickness of 15 nm,shield interval of 0.1 μm, reproducing element width of 0.8 μm) as thereproduction head. The head tilt angle was set to 0°. A signal having alinear recording density of 300 kfci was recorded, and the reproductionsignal was measured with a spectrum analyzer manufactured by ShibaSokuCo., Ltd. In addition, the unit kfci is a unit of linear recordingdensity (cannot be converted to SI unit system). As the signal, asufficiently stabilized portion of the signal after starting the runningof the magnetic tape was used.

One aspect of the invention is advantageous in a technical field ofvarious data storages.

What is claimed is:
 1. A magnetic tape comprising: a non-magneticsupport; and a magnetic layer containing a ferromagnetic powder, whereinan edge portion Ra which is an arithmetic average roughness Ra measuredat an edge portion of a surface of the magnetic layer is 1.50 nm orless, a central portion Ra which is an arithmetic average roughness Rameasured at a central portion of the surface of the magnetic layer is0.30 nm to 1.30 nm, and a Ra ratio (central portion Ra/edge portion Ra)is 0.75 to 0.95.
 2. The magnetic tape according to claim 1, furthercomprising: a non-magnetic layer containing a non-magnetic powderbetween the non-magnetic support and the magnetic layer.
 3. The magnetictape according to claim 2, wherein the non-magnetic powder contains aFe-based inorganic oxide powder having an average particle volume of2.0×10⁻⁶ μm³ or less.
 4. The magnetic tape according to claim 2, whereinthe non-magnetic powder contains carbon black having a pH of 5.0 orless.
 5. The magnetic tape according to claim 2, wherein thenon-magnetic powder contains a Fe-based inorganic oxide powder having anaverage particle volume of 2.0×10⁻⁶ μm³ or less and carbon black havinga pH of 5.0 or less.
 6. The magnetic tape according to claim 1, whereina standard deviation of curvature of the magnetic tape in a longitudinaldirection is 5 mm/m or less.
 7. The magnetic tape according to claim 2,wherein the non-magnetic powder contains a Fe-based inorganic oxidepowder having an average particle volume of 2.0×10⁻⁶ μm³ or less andcarbon black having a pH of 5.0 or less, and a standard deviation ofcurvature of the magnetic tape in a longitudinal direction is 5 mm/m orless.
 8. The magnetic tape according to claim 1, further comprising: aback coating layer containing a non-magnetic powder on a surface side ofthe non-magnetic support opposite to a surface side provided with themagnetic layer.
 9. The magnetic tape according to claim 1, wherein atape thickness is 5.2 μm or less.
 10. The magnetic tape according toclaim 1, wherein a vertical squareness ratio of the magnetic tape is0.60 or more.
 11. The magnetic tape according to claim 2, wherein thenon-magnetic powder contains a Fe-based inorganic oxide powder having anaverage particle volume of 2.0×10⁻⁶ μm³ or less and carbon black havinga pH of 5.0 or less, a standard deviation of curvature of the magnetictape in a longitudinal direction is 5 mm/m or less, a tape thickness is5.2 μm or less, and a vertical squareness ratio of the magnetic tape is0.60 or more.
 12. A magnetic tape cartridge comprising: the magnetictape according to claim
 1. 13. A magnetic tape device comprising: themagnetic tape according to claim
 1. 14. The magnetic tape deviceaccording to claim 13, further comprising: a magnetic head, wherein themagnetic head includes a module including an element array having aplurality of magnetic head elements between a pair of servo signalreading elements, and the magnetic tape device changes an angle θ formedby an axis of the element array with respect to a width direction of themagnetic tape during running of the magnetic tape in the magnetic tapedevice.